8 
erence on dead food or decayed flesh; but the class of garbage-eaters 
may be made to include three or four of the catfishes also, which resort 
to such food willingly when it is convenient to them. Certainly fishes 
in whose stomachs we have found, from time to time, distillery slops, 
ham bones, dead rats, dead cats, and heads and entrails of fish thrown 
out from fish boats, need not complain if they are provisionally assigned 
to the humble class of scavengers. 
These same catfishes might perhaps be better classed as omnivorous, 
for they eat, in fact, very nearly every kind of food which the water 
contains, including insects, mollusks, fishes, crawfishes, and sometimes 
unusual quantities of alge and other aquatic vegetation. In this omnivo- 
rous class we may also place the common European carp, except that this 
fish does not eat carrion. 
If, now, we review the generalities and the peculiarities of food 
and feeding habits which I have imperfectly sketched, seeking to under- 
stand their differentiation and, succession, we may best interpret the 
facts by attempting to realize the food resources of an average, typical, 
undifferentiated fish, which should reach adult condition without acquir- 
ing any special adaptations of structure or of preference in respect to the 
choice, appropriation, and assimilation of its food. Such an undiffer- 
entiated fish would have a subcylindrical body with only the ordinary 
equipment for locomotion; it would be toothless both as to its jaws and 
its pharyngeal bones; its mouth would be neither suctorial nor especially 
protractile; and its gill-arches would be without specialized gill-rakers. 
In other words, it would be a simple product of growth, without progress 
or differentiation, from the state of the recently hatched fry. Such a 
fish would necessarily begin, as all our fishes now do, with a mixed 
plankton for its earliest food, taking the smaller organisms first and the 
larger ones later. As it gradually becomes too large for the pursuit of so 
minute a prey, and its gill structures too coarse to serve longer as a plank- 
ton strainer, it would draw next upon the insects, and mainly on the 
insect larve of the bottom and the shores—creatures especially avail- 
able to it because their soft and poorly protected bodies make them fit 
for digestion without mastication or other special preparation; and with 
these it might mingle also amphipod crustaceans, and the smaller thin- 
shelled mollusks, especially those which could be picked from an aquatic 
vegetation. Next would come such young fishes as it could seize and 
swallow without a special armature of jaws and throat; and at this stage 
of growth and progress it would apparently stop. To go farther as a 
