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 algae 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 larvae 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 



