Comparative Anatomy Chart

Earthworm Frog Snake Shark Perch Pigeon Pig

Circulatory System

Earthworm Capillaries are very near the surface. Longitudinal vessels run throughout the body. The smaller vessels run into a muscular dorsal vessel, which pumps the blood. Five pairs of hearts provide the irregular contractions.
Frog One primitive atrium with two chambers -- oxygen-rich blood travels from the lungs to atrium and 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.
Snake 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 atrium and other ventricle (or the same ventricle if it is a three-chambered heart) and to the body's tissues.
Shark The shark has a single heart of four chambers. Oxygen-poor blood is pumped through one atrium-ventricle pair to the lungs, and the oxygenated blood is pumped through the other pair to the tissues.
Perch Heart consists of one atrium and one ventricle. Oxygen-poor blood is pumped through the heart and to the lungs. After it is oxygenated, it goes directly to the tissues. It then travels back to the heart.
Pigeon The atria and ventricles are in seperate chambers. One atrium-ventricle pair pumps oxygen-poor blood to the lungs, and the other atrium-ventricle pair pumps oxygenated blood to the tissues.
Pig The atriums and ventricles are in seperate chambers. One atrium-ventricle pair pumps oxygen-poor blood to the lungs, and the other atrium-ventricle pair pumps oxygenated blood to the tissues.


Earthworm Gas exchange through skin -- tubular shape gives it a large surface area, moist skin promotes gas exchange.
Frog Diffusion (if enough oxygen is present), external gills can be used to increase surface area where there is less oxygen.
Snake Evolution of the trachea, epiglottis, and nostrils -- breathe almost entirely through lungs (some through skin). Breathing takes place by lungs changing size.
Shark 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.
Perch Gas exchange takes place in internal gills. Water is drawn over the gill surfaces and gas exchange takes place there.
Pigeon 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.
Pig Air is drawn into the lungs, gas exchange takes place at highly vascularized sacs.


Earthworm Two longitudinal nerve cords are fused together to form a double ventral nerve cord with a ganglion 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.
Frog The frog has a dorsal nervous system. The central nervous system is protected by bones of the 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.
Shark Much like the typical vertebrate nervous system. The entire brain is more stretched out and is surrounded by cartilage
Perch The nervous system is like the typical vertebrate system. The brain is stretched out much like the brain of the shark.
Pigeon Typical vertebrate nervous system. The brain is larger and not elongated -- it is closer to the shape of the mammalian brain, though the surface of the brain is not as convoluted.
Pig Typical vertebrate nervous system. The brain is larger in proportion to the rest of the body and the cerebral cortex is highly convoluted in order to increase surface area and thus allows more brain activity.


Earthworm 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 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
Frog The frog digestive system is much like that of other vertebrates. The food is swallowed and travels 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.
Snake 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 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.
Shark 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 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.
Perch The bony fish digest almost exactly like the snake. One difference is that herbivorous fish have a very underdeveloped intestinal system because of the simplicity of their diet. This is not true of the 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
Pigeon 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.
Pig 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.


Earthworm Nephrostome delivers waste to kidney (nephridium) which excretes through nephropore. Worms are 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.
Frog 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 can fill almost the entire body when ovulating. Deposits eggs into dilated uterus through oviduct, and then expells them through cloaca.
Snake Elongated kidneys and testes, no urinary bladder. Testes, ovaries and kidneys are all paired. Few eggs produced, but they are large-- lots of yolk. Sperm ducts end in two hemi-penises at posterior end of body.
Shark 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 in two claspers (penises). Females' ovaries ovulate into oviducts which dilate to become a "uterus", and empty through cloaca.
Perch Kidney is a long dorsal organ-- deposits urine into a urinary duct that leads to bladder-- excretes the urine through a urogenital sinus. The gonad, male or female, empties into the urogenital sinus.
Pigeon Large, paired, irregularly lobed kidneys. Ureter opens into cloaca. Male-- Paired testes in upper abdomen. Ductus deferens empty into cloaca. Female-- Right ovary and oviduct become vestigial. Oviduct secretes hormones over eggs.
Pig 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 uterine tubes lead to a uterus-- opens to the outside through the vagina and urogenital sinus. Excretory system is exactly like a human's.