COMPARATIVE ANATOMY LAB:
FISH AND MAMMAL
This lab write-up contains only these sections in order:
I.
4 Drawing as noted in lab: Draw, label and color.
II.
Answers to lab questions. Use complete sentences, numbered and labeled as in lab.
III.
Comparative Anatomy and Physiology Section, see explanation at end of lab.
Introduction
There are similarities among all vertebrates, which is not surprising since vertebrates have evolved from
common ancestors. Functions such as digestion, locomotion, sensing the environment, and reproduction
are seen throughout the animal kingdom. In vertebrates, the structures that perform these functions may be
somewhat similar. Two representative vertebrates will be used to compare such adaptations: the dogfish
shark and the cat. This comprehensive lab allows the student to apply concepts learned in this class to
make a detailed analysis of similarities and differences among two vertebrates.
Each larger group of 8 students will be divided into two sub-groups. Each group of 8 will share one shark
and one cat. Each group will use two tables, an inner “wet” table and an outer “dry” table. This lab can be
done with specimens and photos, or with photos only. Once the lab is complete, all sections should be
titled, and this handout is not turned in. Each student turns in their own lab, answers are in the student’s
own words.
Do not remove any organs unless specified, you will be asked to show locations of organs in relation to
other organs.
Safety:
GOGGLES MUST BE WORN
DISPOSABLE GLOVES MUST BE WORN
TREAT PRESERVED ANIMALS, THE PRESERVATIVE SOLUTION, AND ALL EQUIPMENT
THAT TOUCHES THE ORGANISM AS POTENTIAL HEALTH HAZARDS. WASH HANDS WITH
SOAP AND WATER AT CONCLUSION OF DAILY ACTIVIES.
Materials:
Dissecting Kit
Dogfish Shark Specimen
Colored Pencils
Cat Specimen
Goggles
OLD CLOTHES OR A COVER-UP SHIRT ARE RECOMMENDED
Preparation:
1. From Photo Manual and Dissection Guide of the Cat, Read page 1-3 Introduction: “The Cat and Man”
and “Anatomical Terminology”.
2. View “Cat Dissection” video, the introduction and other sections pertaining to the dissections you will be
responsible for.
3. When using the book along with the dissection, keep the book on a different table, protected with a clear
plastic bag.
4. The cats have been delivered in plastic bags containing an excess of embalming fluid. Cut the bag at one
end and preserve the fluid in the bag. This bag will be used for storage, so it is important to save the bag
and this formalin solution to keep the cat from drying out.
5. When the cat is removed, it may have a label indicating whether it is male or female, make a note of the
sex. Review pages 5-7 orally with your lab partners, so that you are familiar with directions and regions as
they are described.
Comparing the External Anatomy of Shark and Cat
6. Locomotion: Locate the pelvic fins and the pectoral fins of the shark.
a) How are the structures of locomotion adapted for the habitat of each organism? b) Are the fins of fish
homologous or analogous to the limbs of cats? c) Are the limbs of cats homologous or analogous to the
limbs of humans? How can you tell? d) Human locomotion is plantigrade while cats are digitigrade. How
do these terms differ?
7. Sensory: a) Which sensory system is visible on the cat’s head that is not found in humans? Which type of
information does this system receive (chemical, mechanical, light)? b) The shark has a lateral line
system. What is the function of the lateral line system (hearing is not an accurate answer)? c) Where is the
shark’s lateral line system?
8. Respiratory: a)Locate the nares and the spiracles of the shark. What is the function of each of these?
Use a probe to enter the spiracles. b) Where does the spiracle lead? c) Which of these is also found in the
mammal?
9. Digestive and Urinary: Locate the cloaca of the shark. a) What is the difference between the shark’s
cloaca and the anus of a cat?
Comparing the Internal Anatomy of the Shark and Cat
10. Where to cut:
Shark: Using the scalpel, begin cutting just anterior to the pelvic fins, making the cut to the right of the
midventral line. Continue cutting anteriorly until you reach the pectoral fins. Make two transverse cuts
across the body, one just posterior to the pectoral fin, and the other just anterior to the pelvic fins. You
have exposed the pleuroperitoneal cavity (this word means the joint lung and abdominal cavity).
Cat: When cutting, you will penetrate the muscle layer, so that the internal organs are exposed. Using the
scalpel, carefully cut up the midventral line, from the posterior side of the hind limbs, to the anterior side of
the forelimbs. Make two transverse cuts across the body, one anterior to the midventral cut, and one
posterior to the midventral cut. Try to keep the omentum intact. The omentum is a layer of connective
tissue and fat. This is the belly fat that is a problem for many humans. It is said that a larger omentum
increases appetite, so this is an example of positive feedback.
See attached illustrations for details about the shark’s abdominal cavity.
See pages 79-85 in the cat book for details about the cat’s abdominal cavity.
11. Internal Digestive System:
a) How are the shark’s teeth different from the cat’s teeth? Homodont dentition means all the teeth have
the same shape. Do sharks or cats have homodont dentition?
Locate the shark’s liver. a) How many lobes of the liver can you see? Can you find the gall bladder of the
shark? Cut through the omentum and locate the cat’s liver. b) How many lobes are seen in the cat? c)
Name the lobes of the cat’s liver. d) What are the functions of the liver and gall bladder, which are
basically the same for both organisms. Cut open the valvular intestine of the shark to observe the spiral
valve. e) The purpose of the spiral valve is to increase ___________, which is the same reason for folding
of the intestines of mammals.
Cut through the cat’s throat to locate the trachea, which is ribbed and tough. To its left, find the esophagus.
Trace the esophagus to the stomach and then to the intestines. f) How can one distinguish between the
small and large intestines. (We will observe the stomach contents of each later).
Drawing 1-Abdominal Cavity of Shark. Draw label and color your shark.
Drawing 2 Abdominal Cavity of Cat. Draw and label your cat.
Your goal is to see as much as possible, however, you must draw your own specimen if you are using a
specimen. If you can’t see it, don’t draw it.
Liver (brown), Gallbladder (green), stomach (yellow), Pancreas (purple), Intestines (pink), Spleen (red)
12. Heart
To view the shark’s heart within the pericardial cavity, continue your original ventral cut anteriorly through
the pectoral girdle and the surrounding muscles. Make a transverse cut just below the mouth and fold back
the flaps.
Using the shark heart diagram, locate the following in your shark: Ventricle, Conus arteriosus, Atrium, and
Sinus venosus. a) Put the above structures in the order that blood will pass through. Use the text below the
heart diagram for this. b) What is the one major difference between the blood in a shark’s heart and the
blood in a mammal’s heart?
Notice how the cat’s heart is oriented and connected to the lungs.
You may now remove and dissect the cat’s heart, keeping track of which side was ventral. Observe the
pericardium, the membrane surrounding the heart. Cut the heart in half, in a frontal plane, meaning cut the
ventral and dorsal halves apart. Locate the 4 chambers of the heart. c) The walls of which chamber are the
thickest, to pump blood through the entire body?
13. Gills/Lungs
Notice the orientation of the lungs of the cat, and the gills of the shark.
a) In the fish, oxygen is received in water through the _________ and the water exits through the _____.
b) To increase the diffusion of oxygen, blood and water flow in opposite directions, a process called
_____________________________________.
c) The interior of the gills is composed of layers of tissue called lamellae, which is where gas exchange
occurs. What do you think happens to these lamellae if the fish is removed from water?
14. Urogenital System:
Drawing 3-UROGENITAL SYSTEM OF CAT. Draw, color and label your cat. Use the diagrams and
text on pages 123-133 to help you label as below, and answer questions about the cat reproductive system.
Drawing 4- UROGENITAL SYSTEM OF SHARK. Draw, color and label the UROGENITAL
SYSTEM of your shark. See diagrams for help.
Male: Testes (yellow), Ductus deferens (green), Kidney (red), Ureter-cat only (blue), Urinary bladder-cat only (pink).
Female: Ovaries (yellow), Oviducts (green), Uterus (orange), Ureter- cat only (blue), Urinary bladder-cat only (pink).
a) Why are multiple births (a litter) more common in cats than in humans?
b) Describe a malady involving the testes that is relatively common in humans, but not seen in cats. Why
would this be?
c. Cats are viviparous. Define each of the following terms and find out which applies to dogfish sharks:
viviparous, oviparous, or ovoviviparous.
15. Remove the stomach of each organism. Carefully clean out the stomach contents of each organism. a)
Write observations about what you see in the stomach contents for each. b) The cat has folds in the stomach
called rugae, to increase _________. c) Does the shark have rugae?
16. CLASSIFICATION
SHARK
CAT
What is the KINGDOM?
What is the PHYLUM
What is the CLASS
Name 5 CHARACTERISTICS of this
class, that you observed in your
specimen.
List 3 other EXAMPLES of
organisms that belong to the SAME
CLASS
Name 1 EXAMPLE of an
organism in the same phylum that
DOES NOT
belong to this class.
III. Comparative Anatomy and Physiology:
Write a 2-3 paragraph comparison of your findings. Discuss the similarities and differences in the anatomy
and physiology of the shark and human. You should include facts learned during lab and “discoveries” that
your group made. You may include information we learned in class and that which is found in the
textbook. Remember that we also watched parts of a video about the cat.
Compare the external anatomy, and the systems that were observed in this lab, and any other observations
that you made. Please bring in additional information about cat and shark anatomy or behavior to receive
an “A” paper.
Sources:
Dogfish Dissection Manual, Wingard, Bruce D., The Johns Hopkins University Press, 1988
Photo Manual and Dissection Guide of the Cat, Bohensky, Fred, Square One Anatomy, 2002