Comparative Anatomy Chart
Earthworm Frog Snake Shark Perch Pigeon Pig
Circulatory System
Capillaries are very near the surface. Longitudinal vessels run throughout the body. The smaller
Earthworm vessels run into a muscular dorsal vessel, which pumps the blood. Five pairs of hearts provide the
irregular contractions.
One primitive atrium with two chambers -- oxygen-rich blood travels from the lungs to atrium and
Frog
oxygen-poor blood is brought from the tissues back to the atrium. Both types are pumped through
the ventricle, but there is no mixing of the oxygen-rich and oxygen-poor blood.
Snakes have either a three-or four chambered heart. Oxygen-poor blood is pumped through one
atrium and the ventricle and to the lungs. Oxygenated blood is then pumped through the other
Snake
atrium and other ventricle (or the same ventricle if it is a three-chambered heart) and to the body's
tissues.
The shark has a single heart of four chambers. Oxygen-poor blood is pumped through one atriumShark
ventricle pair to the lungs, and the oxygenated blood is pumped through the other pair to the tissues.
Heart consists of one atrium and one ventricle. Oxygen-poor blood is pumped through the heart and
Perch
to the lungs. After it is oxygenated, it goes directly to the tissues. It then travels back to the heart.
The atria and ventricles are in seperate chambers. One atrium-ventricle pair pumps oxygen-poor
Pigeon
blood to the lungs, and the other atrium-ventricle pair pumps oxygenated blood to the tissues.
The atriums and ventricles are in seperate chambers. One atrium-ventricle pair pumps oxygen-poor
Pig
blood to the lungs, and the other atrium-ventricle pair pumps oxygenated blood to the tissues.
Respiration
Earthworm
Frog
Snake
Shark
Perch
Pigeon
Pig
Gas exchange through skin -- tubular shape gives it a large surface area, moist skin promotes gas
exchange.
Diffusion (if enough oxygen is present), external gills can be used to increase surface area where
there is less oxygen.
Evolution of the trachea, epiglottis, and nostrils -- breathe almost entirely through lungs (some
through skin). Breathing takes place by lungs changing size.
Internal gills increase surface area with a lesser chance for damage than the external gills. They do
not have the capability to draw water over the gills, so they must always be moving or in moving
water so that fresh water passes over the gills.
Gas exchange takes place in internal gills. Water is drawn over the gill surfaces and gas exchange
takes place there.
Each lung has several air sacs attached to it. No actual gas exchange occurs in the air sacs. Instead
they draw larger amounts of air through the lungs than the lungs could unaided and allow a greater
amount of gas exchange to occur.
Air is drawn into the lungs, gas exchange takes place at highly vascularized sacs.
Nervous
Two longitudinal nerve cords are fused together to form a double ventral nerve cord with a ganglion
Earthworm in each body segment. The nerve cord branches out into two separate cords just below the pharynx
and they meet again in the head, ending as two large dorsal ganglia.
The frog has a dorsal nervous system. The central nervous system is protected by bones of the
Frog
vertebral column and the skull. The brain consists of the forebrain (cerebrum and thalamus),
midbrain (optic lobe), and hindbrain (cerebellum and medulla oblongata).
Snake
Much like the system of the frog, but the forebrain is larger and more elongated.
Much like the typical vertebrate nervous system. The entire brain is more stretched out and is
Shark
surrounded by cartilage
The nervous system is like the typical vertebrate system. The brain is stretched out much like the
Perch
brain of the shark.
Typical vertebrate nervous system. The brain is larger and not elongated -- it is closer to the shape
Pigeon
of the mammalian brain, though the surface of the brain is not as convoluted.
Typical vertebrate nervous system. The brain is larger in proportion to the rest of the body and the
Pig
cerebral cortex is highly convoluted in order to increase surface area and thus allows more brain
activity.
Digestive
The earthworm is the only invertebrate we dissected. It is one of the earlier evolving 1-way
digestive systems. Food (decaying vegetation) enters the mouth and is stored in the crop until it can
Earthworm be emulsified in the gizzard with the aid of soil particles. the rest is an extended, unconvoluted
intestine (gut) which breaks down and absorbs the nutrients. The remnants are expelled from the
anus
The frog digestive system is much like that of other vertebrates. The food is swallowed and travels
Frog
down the esophagus, where it is digested. It is then neutralized by the gall bladder and nutrients are
absorbed from the chime in the intestines.
The snake's digestive system is similar to that of most other vertebrates. Food (small animals) enters
through the mouth. It is carried down the esophagus and digested in the stomach which after
completing digestion, is neutralized by the gall bladder. The chime (as the digested food is called) is
Snake
further digested and absorbed by the intestine. The intestine is unconvoluted to prevent full
absorption of too large quantities of cholesterol and fat. Feces are then excreted from the cloaca.
The snakes digestive system is elongated because of their body type.
The shark evolved earlier than most animals with a diferent system. After exiting the stomach, the
food enters the duodenum. Then it travels in the valvular intestine. This is the evolutionary
Shark
difference. Instead of having an intestine that is externally convoluted, the valvular intestine is
coiled around itself on the inside. The feces are then excreted from the cloaca.
The bony fish digest almost exactly like the snake. One difference is that herbivorous fish have a
Perch
very underdeveloped intestinal system because of the simplicity of their diet. This is not true of the
Pigeon
Pig
carnivorous Perch. The only unilateral difference of fish is that they have two openings of excretion,
unlike the cloaca of many other animals. The rectum and the anus
The pigeon is nearly exactly similar to the other vertebrates with slight evolutionary variations
according to their diet. Birds have no teeth and utilize a gizzard with soil particles (like the
earthworm) to break down the tough seeds and vegetation which they consume.
The pig's digestive system is nearly identical to that of a human, both evolutionarily and dietarily. It
has teeth to masticate bolus (as masticated food is called) before it enters the esophagus. The pig
also has the classic vertebrate digestive system and extremely convoluted intestinal tract to extract
the maximum amount of nutrients from the vegetation of this omnivore.
Urogenital
Nephrostome delivers waste to kidney (nephridium) which excretes through nephropore. Worms are
Earthworm hermaphrodites-- three pairs of seminal vesicles which contain testes. Ovaries are outside vesicles.
Oviducts and deferens join before expulsion of sperm and release of eggs.
Kidneys empty urine into bladder via archinephric ducts which empty into cloaca. Male-- testes use
same duct as the kidneys to deliver sperm to the cloaca. Female-- ovaries are very large organs that
Frog
can fill almost the entire body when ovulating. Deposits eggs into dilated uterus through oviduct,
and then expells them through cloaca.
Elongated kidneys and testes, no urinary bladder. Testes, ovaries and kidneys are all paired. Few
Snake
eggs produced, but they are large-- lots of yolk. Sperm ducts end in two hemi-penises at posterior
end of body.
Kidneys and genitals empty into common organ, the cloaca. Kidneys are long dorsal organs-- only
posterior end is functional. Testes are similarly shaped organs that, after passing through cloaca, end
Shark
in two claspers (penises). Females' ovaries ovulate into oviducts which dilate to become a "uterus",
and empty through cloaca.
Kidney is a long dorsal organ-- deposits urine into a urinary duct that leads to bladder-- excretes the
Perch
urine through a urogenital sinus. The gonad, male or female, empties into the urogenital sinus.
Large, paired, irregularly lobed kidneys. Ureter opens into cloaca. Male-- Paired testes in upper
Pigeon
abdomen. Ductus deferens empty into cloaca. Female-- Right ovary and oviduct become vestigial.
Oviduct secretes hormones over eggs.
Male-- Only one testis, very similar to a human's-- the testis leads to epidydimis, vas deferens,
seminal vesicles, and then urethra. Female-- also very similar to a human's-- two ovaries whose
Pig
uterine tubes lead to a uterus-- opens to the outside through the vagina and urogenital sinus.
Excretory system is exactly like a human's.