28 The Dissection of the Fish 
not be homologous with abdominal pores. In most other bony 
fishes the testes and ovaries are continued directly into ducts 
which open to the outside. 
Organs of Nutrition.—The organs thus shown in dissection 
we may now examine in detail. 
The mouth of the fish is the organ or series of structures first 
concerned in nutrition, The teeth are outgrowths from the 
Fic. 17.—Black Swallower, Chiasmodon niger Johnson, containing a fish larger 
than itself. Le Have Bank, 
skin, primarily as modified papillz, aiding the mouth in its various 
functions of seizing, holding, cutting, or crushing the various kinds 
of food material. Some fishes feed exclusively on plants, some 
on plants and animals alike, some exclusively on animals, some 
on the mud in which minute plants and animals occur. The 
majority of fishes feed on other fishes, and without much regard 
to species or condition. With the carnivorous fishes, to feed repre- 
sents the chief activity of the organism. In proportion to the 
voracity of the fish is usually the size of the mouth, the sharp- 
ness of the teeth, and the length of the lower jaw. 
The most usual type of teeth among fishes is that of villiform 
bands. Villiform teeth are short, slender, even, close-set, making 
a rough velvety surface. When the teeth are larger and more 
widely separated, they are called cardiform, like the teeth of a 
wool-card. Granular teeth are small, blunt, and sand-like. Ca- 
nine teeth are those projecting above the level of the others, 
usually sharp, curved, and in some species barbed. Sometimes 
