CATOSTOMID.E THE SUCKERS 63 



average frequency of this joint occurrence of the species of 

 suckers and buffaloes in collections is decidedly greater, accord- 

 ing to our experience, .than the corresponding average for the 

 darters or the sunfish, being represented, for suckers, by the 

 general coefficient of 2.45, for darters by 2.02, and for sunfish 

 that is, the Centrarchidce exclusive of the black bass by 1.87. 



When full grown, the majority of the species are safe from 

 any enemies of their kind which the water contains, but their 

 survival to adult age is dependent on their fortune in escaping 

 from a host of predaceous and voracious fishes against which 

 they have no defense, and to whose depredations their haunts 

 and habits freely expose them. In the food of 1,221 Illinois 

 fishes, representing 87 species, studied by the senior author 

 during the dozen years preceding 1888, suckers and buffalo-fish 

 were found most frequently in the food of the pike, but occurred 

 also in that of dogfish, bullheads, sheepsheads, and sunfish. 

 The sucker family would evidently suffer much more severely, 

 however, if it were not for the presence in the waters they in- 

 habit of the gizzard-shad, more abundant, and probably more 

 accessible to pike and other predaceous fishes, than are either 

 suckers or young buffaloes. It is an interesting illustration of 

 the way in which companion species having little or nothing to 

 do with each other directly may nevertheless greatly influence 

 each others' welfare, that while 20 pike out of 37 had eaten 

 gizzard-shad, which made, in fact, nearly half the food of the 

 entire number, only 3 per cent, of their food came from the sucker 

 family, and this had been eaten only by three of the pike. 



Examining the other side of the food relation, we find that 

 the food of this family itself, as illustrated by a careful study of 

 the stomach contents of 109 specimens, belonging to five genera 

 and eleven species, consisted mainly of the smaller mollusks 

 living in the mud and larvae of aquatic insects, the two being 

 about equal in ratio and together making more than three fourths 

 of the entire food. Vegetation contributed less than 10 per cent, 

 to the mass examined, and no element of this class was especially 

 prominent. 



The structures of alimentation vary noticeably in definite 

 directions as one passes along the series from the most cylindrical 

 suckers to the thin and deep-bodied buffalo and carp. In the 

 former the pharyngeal bones are heavy, and the lower teeth are 

 thick and strong, usually with a well-developed grinding surface, 

 while the gill-rakers are short, thick, and few, and the intestine is 



