As different as a man may be from a fish, both life forms share some similarities in basic structure and functions. Man and fish share such organs as the brain, stomach, liver, and kidneys. Other organs appear in different forms in different organisms; for example, the lungs in humans and the gills in fish are very different but both provide the same basic function of respiration. Finally, some organs are simply not present in man, such as the fish's swim bladder. The following illustration of a Paradise Fish (Macropodus opercularis) shows some of the common internal features of the fish.

The Blood:
If the blood was to be examined, the nucleus cell of the blood can be nicely observed under the microscope. Most of the cells found in the blood are red blood corpuscles (erythrocytes), and only a very few are white blood corpuscles (leukocytes). Fish red blood cells contain nuclei, mammalian do not. If viewed under a microscope the slide mount would show the erythrocytes lying flat next to one another, and cells that are standing on edge look like dumbbells.

Internal Anatomy