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Practical Three -Toad dissection Prac
Evolutionary and Functional Biology (University of New South Wales)
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Campbell, N.A. & Reece, J.A. et al. (2014). Biology, 10th Edition (Australian Version),
Benjamin/Cummings, San Francisco
Chapter 40 - Basic Principles of Animal Form and Function
Chapter 41 – Animal Nutrition
Chapter 42 – Circulation and Gas Exchange
Chapter 46 – Animal Reproduction
The aim of this practical is to introduce you to the gross morphology and anatomy of the
vertebrates, with a specific focus on animal organs and organ systems.
Learning Objectives
By the end of this practical, you will be able to:
1. Outline the basic gross morphology and anatomy (external and internal) of an amphibian (toad).
2. Identify, name and describe the function of the major vertebrate organs and organ systems
(digestive, respiratory, circulatory, urogenital and reproductive).
3. Identify the basic cell types (muscle, connective and epithelial tissue) that comprise animal tissues
and organs.
4. Relate the function of a structure to its anatomy.
5. Explain how behaviour, physiology and ecology influence form and function.
6. To learn the biological technical skill of dissection.
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In the two practicals on animal structure (Practicals 3 and 4), there are four levels of biological
organisation to be examined – organs, organ systems, cells and tissues. Most emphasis will be
placed on organs and tissues. In Animal Structure 1 (this practical- practical 3) you will examine the
shape, size, location and relationships of the major organ systems as well as the anatomical features
of amphibians (Cane Toad Bufo marinus). In Animal Structure 2 (the next practical- practical 4) you
will make similar examinations of mammals (laboratory rat Rattus norvegicus). This will allow you to
compare the gross morphologies and anatomy of two species from different vertebrate classes that
exhibit different behaviour, physiology and ecology.
In this practical you will examine:
1. The Digestive System
2. The Respiratory and Circulatory Systems
3. The Excretory and Reproductive Systems.
4. Histology: the basic cell types (muscle, connective and epithelial tissue) that comprise animal
tissues and organs.
Study species Scientific name:
Bufo marinus
Common name: the Cane toad
Cane toads (Bufo marinus) are native to South and Central America. The cane toad was first
introduced to Australia in 1935 as a biological control to combat cane beetle populations on
sugarcane farms in Queensland. Since its introduction to the Australian landscape, the cane toad
has adapted and evolved, voraciously consuming native wildlife and killing predators with its toxic
skin. With no predators or disease to control cane toad numbers, the cane toad itself is now
considered a pest species and its introduction to Australia has been deemed as an ecological
disaster. In 2005, the biological effects, including lethal toxic ingestion, caused by Cane Toads (Bufo
marinus) was listed as a key threatening process under the Environment Protection and Biodiversity
Conservation Act 1999. The cane toads that you will be dissecting in class today have been collected
as part of a cane toad removal project.
Interesting toad facts
Toads and frogs are both in the order Anura.
There are some key differences between toads and frogs. Toads are associated with a drier,
wart-covered, leathery skin, and shorter legs than frogs. They also can live further away from
Toads are usually nocturnal. They burrow beneath the earth in the day and come out at night to
feed on insects, amphibians, reptiles and mammals.
Toads do not like the cold and hibernate throughout the winter months.
In the wild, most toads species live an average 3 of to 5 years.
Toads have a pair of parotoid glands on the back of their heads. These glands and their skin in
general, contain a poison (bufotoxin) which the toad excretes if feeling stressed or threatened.
The poison excreted by the cane toad can cause severe irritation and fatality if ingested. It is
important to always remember to wash your hands after touching a toad- do not put your
hands anywhere near your mouth.
Contrary to popular believe you will not get warts by touching the bumpy wart-like skin or
glands of a toad, however you should always wash your hands after touching a toad.
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Work Schedule
Work in pairs. In your group you should have a male and female toad. If you do not have both sexes,
let a demonstrator know as you will be examined on both in the practical exam.
Start by examining the external features of the toad and answer the associated questions in your lab
manual. Once the external features have been covered your lab supervisor will guide you through
the dissection process.
Use the toad diagram (provided on the last page of Practical 3) to help locate and identify organs in
the toad. Make sure you take lots of notes and draw lots of diagrams; these will help you to study for
the practical exam and aid you in your assessment task next week (practical 4).
Equipment required: Specimen, dissection tray, pins, blunt probe, blunt tweezers, dissection
scissors, microscope, practical notes, pencils, rubber and pens for taking notes. You can take photos
for your study notes during the class.
1. The External Features
Examine the external features of the toad, noting the rough warty skin, nares, tympanum and
parotoid (suprascapular) glands.
Parotoid (suprascapular) glands secrete poison, so refrain
hereafter from touching your mouth, eyes and so on, until
you have thoroughly washed your hands.
Describe the BODY SURFACE (texture, moisture, epidermal lesions, covering) of the toad.
Outline the function(s) of the skin in a cane toad.
Note the structures involved in smell, sight, hearing and touch. They also relate to the ability of the
animal to obtain food. Note the size and shape of the body and limbs. They relate to the types of
movement possible in the procurement of food and to the types of food procurable.
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Describe the location, shape and size of the eyes.
Describe the location, shape and size of the nares (nostrils).
The tympanum (ear cavity or ear drum) is an external hearing structure in animals such
as mammals, birds, some reptiles, some amphibians and some insects.
In toads and frogs, the tympanum is a large external oval shape membrane made up of nonglandular skin which is located just behind the eye. It does not process sound waves; it simply
transmits them to the inner parts of the amphibian's ear which is protected from the entry of water
and other foreign objects.
Examine the tympanum of the toad. Make sure you can easily distinguish it from the parotoid
(suprascapular) poison glands.
Examine the parotoid poison gland. Describe the location, size, shape and function of this gland.
Turn the toad over onto its back (with the belly facing upwards). Pick up a blunt dissecting probe and
gently use it to open the toad’s mouth. You may need to do this in pairs, with one person holding the
toad and the other opening its mouth.
Examine the toads tongue. Is the tongue attached to the front or the back of the lower jaw?
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Can you see any teeth? Try running your finger along the upper jaw (maxilla) and lower jaw
(mandible) of your specimen or one of the skeletons on the front bench. Are there teeth? Where?
What size?
Describe how the toad catches, chews and swallows food. How does this relate to the point of
attachment of the tongue?
Your supervisor will now show you a short video on cane toads from the curiosity show.
After watching the video can you tell the sex of the toad from its external features? Presumably
toads have no difficulty with this, but humans find it difficult. Refer to the posters around the room
for extra information.
What are nuptial pads? Are they found on the male or female toad?
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Notes on Dissection Technique
A good dissection is one in which the different parts of an organism have been separated clearly to
show their relationship one to the other.
Keep your dissecting instruments in good order. Wash or wipe them carefully after use and dry them
before putting them away. You may wish to coat them with a thin layer of vaseline petroleum jelly to
prevent rust. Do not use dissecting instruments for any other purpose.
During dissection care should be taken not to destroy or damage any structures inadvertently, and
thus, it is important to use the correct instruments for particular tasks:
Use only heavy round-pointed scissors for cutting tough material such as skin, thick muscle or
thin bones.
Use forceps or fine pointed scissors for freeing delicate structures such as small blood vessels
and nerves from surrounding tissues.
Use blunt seekers (probes) to trace pathways of nerves and blood vessels or for lifting delicate
Barrier cream is provided to protect your hands but students with sensitive skins may prefer to wear
provided surgical gloves.
Your supervisor will now instruct you on the techniques of dissection. Please
follow the instructions directly, if you fall behind or need help, simply put up
your hand and a demonstrator will come to your aid.
2. The Digestive system
The gastrointestinal tract, also called digestive tract or alimentary canal, is the pathway by which
food enters the body and solid wastes are expelled. The gastrointestinal tract includes
the mouth, pharynx, oesophagus, stomach, small intestine, large intestine, and anus.
The digestive system is made up of the digestive tract and other organs that help the body break
down and absorb food.
Taking care not to tear the mesenteries (the thin connective tissue membranes holding viscera in
place), identify the following regions of the digestive system (gastrointestinal tract and associated
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Oesophagus: The oesophagus is a short, narrow, tubular structure that begins in the posterior
portion of the mouth cavity (pharynx) and carries food from there to the stomach.
Stomach: The stomach is a structure where food is broken down chemically (by enzymes in an acid
medium) before entering the small intestine. The stomach is divided into anterior cardiac and
posterior fundic and pyloric regions. The pyloric sphincter muscle is at the posterior end of the
stomach and regulates the entry of food into the small intestine.
Duodenum: The duodenum forms a U-shaped loop that surrounds the pancreas. Food is further
digested in the presence of chemical entities from the pancreas and liver in the duodenum.
Small intestine: The small intestine is a thin, irregularly coiled, tubular structure leading off the
posterior end of the stomach (passage of food from stomach to intestine is regulated by the pyloric
sphincter at this point). The first part of the small intestine is the duodenum. The bile duct and
pancreatic duct enter the duodenum just beyond the pyloric sphincter and carry chemical products
that cause further digestion of food in the duodenum.
Large intestine: The large intestine is the terminal section of the alimentary tract and is
distinguished from the small intestine by its greater diameter and thinner wall. Waste faecal
material accumulates in this section. In the Rat, the large intestine can be further classified divided
into colon, rectum and anus. The colon is a relatively short portion of the large intestine that has
both an ascending and descending limb. Faecal pellet formation begins in the colon as water is
absorbed back into the bloodstream. The rectum is the terminal expanded region of the alimentary
tract that typically contains faecal pellets. The anus is the terminal orifice through which faeces are
expelled. It is separate from the orifices through which urine and genital products are expelled.
Cloaca: (Toad Only) In the Toad the large intestine narrows down in the pelvic region to form the
cloaca, which also receives urine from the kidneys and the products of the reproductive organs.
Faeces, urine and reproductive products are voided to the exterior through the cloacal aperture.
[Note: if you cannot see the relationship between the ends of the digestive tract and the urogenital
tracts and the cloaca, it may help to make two incisions through the pelvic girdle on either side of
the midline and remove the central portion of the girdle].
Liver: The liver is a large dark red-brown organ in the anterior region of the abdominal cavity. It has
three lobes and lies ventral to the stomach. The liver is the powerhouse of the animal where much
of the energy metabolism takes place. The liver performs several functions and is important in
energy metabolism, detoxification and bile production. It is one of the few organs in the body that
can regenerate its own tissues throughout the life span of the individual. Note, if you have the time,
the remarkable variation in shape of the liver in different individual rats. It is an accommodating
Bile duct: The bile duct is a fine duct that carries bile from the liver to the duodenum.
Gall bladder: (Toad Only) Stores bile. Bile is secreted by the liver and is carried by a small duct to the
gall bladder for storage. Bile, which is synthesised in the liver, is transported directly to the
duodenum where it assists in the emulsification of fats.
Pancreas: The pancreas is located in a mesentery, the thin membrane of the duodenal loop. The
pancreas (acinar portion) produces enzymes that assist in the digestion of food in the small intestine.
They are carried in a small duct that enters the duodenum, but this may be difficult to find. The
pancreas in the Toad is an irregular flattish glandular tissue, yellowish white, while in the Rat it is a
mass of pinkish tissue.
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Study notes and sketches on the digestive system.
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3. Respiratory and Circulatory Systems
The respiratory and circulatory systems work together to circulate blood and oxygen throughout
the body. Air moves in and out of the lungs through the trachea, bronchi, and bronchioles. Blood
moves in and out of the lungs through the pulmonary arteries and veins that connect to the heart.
As the toad is an amphibian, it is able to receive oxygen and given out carbon dioxide from three
kinds of respiratory organs.
(1) The lungs,
(2) The skin, and
(3) The mucous membrane of the buccal cavity.
Like all amphibians, toads breathe through their skin as well as with their lungs. Air enters
the toad's mouth through its nostrils, and by raising the floor of its mouth, the toad forces the air
into its lungs. Note the toad does not have a diaphragm.
Taking care not to damage delicate tissues and blood vessels, identify the following components of
the respiratory and circulatory systems.
Trachea: The trachea can be seen as a flexible, tubular structure with cartilaginous rings, in the neck.
Dissect the trachea and find the cartilaginous rings.
Glottis: the thin opening between the vocal cords at the top of the larynx (= the organ in the throat),
that is closed by the epiglottis when an animal swallows.
Lungs: The lungs are paired, dorsal to the liver, and composed of soft, thin-walled, often shrivelled
tissue. A short bronchus connects each lung to the larynx. Slit open a lung and observe its internal
structure. Note the little pockets or alveoli (singular alveolus) in the lining. These are the sites of gas
exchange. Note, however, that amphibians can also respire through their skin (cutaneous
respiration) as well as their lungs.
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Heart: The heart is a reddish conical, muscular organ that is enclosed within a thin membrane, the
pericardium or pericardial sac. Expose the heart by carefully removing the pericardium. Note the
large single ventricle and two, smaller atria (singular atrium) of the toad heart. Raise and tilt the
ventricle forward to expose the large sac-like sinus venosus.
How many chambers are there in the toad’s heart?
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Study notes and sketches on the respiratory and circulatory systems.
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4. Urogenital System
The reproductive system of the toad is significantly different from that of the rat. The excretory
system (kidneys, ureters, urinary bladder) disposes of liquid wastes. The reproductive system
(gonads and ducts) produces the gametes. These two systems are structurally interrelated in the
toad and other vertebrates and are collectively termed the urogenital system. All parts are paired
except the urinary bladder and cloaca.
5. Excretory system
Kidneys: Kidneys produce urine, ridding the body of metabolic wastes, and are important in
osmoregulation. Associated with the kidneys are adrenal glands, on (or close to) the ventral surface
of each kidney, which are parts of the endocrine system. You will notice soft, finger-like, yellowish
lobes attached to the anterior of the toads kidneys – these are fat bodies.
Ureters: The ureters are two whitish ducts, one along the posterior lateral part of each kidney
leading to the dorsal wall of the urinary bladder. These conduct the liquid urine.
Urinary bladder: The urinary bladder is a single thin-walled sac that collects and stores urine before
it is released from the body.
Study notes and sketches on the urogenital and excretory systems.
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6. Reproductive system
Examine the reproductive system of both male and female toads and rats.
In the male, sperm passes from the testis into the kidney tubules and to the cloaca and exterior
through the ureters. Thus, they are termed urogenital ducts, carrying both urine and sperm. Each
urogenital duct may be expanded at about two thirds of its length so as to store sperm prior to
Identify the testes (singular testis) which are bean-shaped, creamy-yellow coloured organs, each
attached near the kidney by a short mesentery. The testes produce sperm, the male gametes. The
vasa efferentia are several minute ducts leading from each testis through the mesentery to the
kidney. These carry sperm. On the anterior end of each testis is Bidder’s organ which is a nonfunctional, ovary-like structure indicative of incomplete sexual differentiation in amphibian gonads.
Males of some frog species also have a vestigial oviduct.
In the female the ureters do not carry reproductive products (eggs) and thus are termed urinary
ducts. Identify the ovaries which are two hollow lobes that may be small or large and have thin walls
containing egg follicles. The paired oviducts are highly coiled whitish tubes close to the mid-dorsal
line. Each opens from the coelom near the anterior base of a lung by a funnel (or ostium). The
oviducts are posteriorly expanded into ovisacs before entering the cloaca. Eggs escape from the
ovaries into the coelom, are moved by cilia on the peritoneum to the funnels, and thence down the
oviducts where glands in the walls add jelly coats.
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Study notes and sketches on the reproductive organs.
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7. Histology (taking a closer look)
Histology is the study of the microscopic structure of tissues and that is what we are going to
explore next.
Clear and tidy your workspace to make room for the microscopes. Keep 1 dissected toad out per
group of 4 students.
Follow the supervisor’s instructions regarding the use of microscopes.
Muscle Tissue
Three main types of muscle are found in the body.
Striated muscle: (also called skeletal or voluntary muscle). Muscles of this type are attached to the
skeleton by tendons and are under voluntary control. The contracting fibres (fibrils) are aligned in
parallel bundles in the cell, so that their different regions form striations (stripes) which are clearly
visible under the microscope.
Cardiac Muscle: (also called heart muscle or myocardium) constitutes the main muscle tissue of the
walls of the heart and works involuntarily. Cardiac muscle can be distinguished from striated skeletal
muscle in a number of ways with the main distinguishing feature being intercalated disc lying
between cell wall.
Smooth Muscle: muscle tissue in which the contracting fibres are not highly ordered, occurring in
the gut and other internal organs (normally where something passes through). Smooth muscle
appears smooth and not is not under voluntary control. Smooth muscle cells are usually cigar
Types of vertebrate muscle tissue (© Campbell)
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Make drawings of tissues and organs to use as revision material for the practical exam.
A. Striated muscle (voluntary or skeletal)
Where would you find striated muscle in the toad?
You have been given two slides, one of which shows the muscle in longitudinal section (Y7/01/12)
with a yellow stain. It is hard to see the striations with this stain (try 10X and 40X). The other slide
(Z16) is a bit more confusing. It contains connective tissue (pinkish red stain) and skeletal muscle in
both cross section and longitudinal section (dark purple). Under 40X, look for a longitudinal section
and see how beautifully the striations are shown with the purple stain! Make a drawing of a
longitudinal section of a striated muscle (slide Z16) under 40X. Include a scale.
Sketch of striated muscle
B. Cardiac muscle
Examine the handout of cardiac muscle.
Where is cardiac muscle found in the toad?
Have a look at the toad’s heart and think about what the cardiac muscle does.
Why would cardiac muscle cells look different to the cells of other muscle tissue?
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C. Smooth muscle
Where would you find smooth muscle in the toad?
Artery and vein
Examine the artery and vein (Y7/02/13) together under low power. There might also be a cross
section of a nerve in your slide, ignore it. Under 40X, compare the tissue composition of the walls of
both vessels. Nuclei have stained purple to red; smooth muscle takes a heavy red stain; cytoplasm of
endothelial cells takes a light red stain; and connective tissue stains green. Make drawings to the
same scale of cross-sections through an artery and a vein. Show the structures and include a scale.
Drawing of an artery and a vein in cross section- label both clearly
Describe the function of an artery?*
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Describe the function of a vein?*
Arteries and veins are comprised (made up) of what tissue type(s)?
Epithelial Tissue
Epithelial tissue is difficult to find in isolation. Epithelial tissues are sheets of tightly packed cells that
line organs and body cavities. There are three main types of epithelial tissue: squamous, columnar
and cuboidal. Each of these tissue types are illustrated below and further examined as tissue types
that comprise parts of the organs described later in next week’s practical (practical 4).
Types of epithelial tissue (© Campbell).
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A. Squamous epithelial tissue
Squamous, or flattened, epithelial cells compose the walls of the alveoli in
the lung. It is difficult to make a good slide of lung tissue because the
alveolar walls collapse and break. Examine slide Y5/01/3 under low power.
Can you distinguish bronchioles from blood vessels?
Under 40X, examine the cells that form the alveoli. You won’t be able to make out much detail,
except the dark nuclei, but you can see the general shape of these cells.
Why are they so thin?
Sketch a portion of lung tissue at 40X to show basic cell types. Include a scale.
Sketch of lung tissue
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(sinus venosus)
gall bladder
fat bodies
small intestine
large intestine
Figure: Drawing of a dissected male cane toad.
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