10 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



which feed upon such vegetation. Stomach analysis, however, has 

 not been directed toward the recognition of such minute material. 



Number of identifications, 12; percentage of identifications among 

 those of all animals, .0050 ; percentage of species in this phylum among 

 the whole number of animal species known, 1.4272. 



Other enemies.^ — Protozoa are the prey of others of their kind — 

 of bacteria, of rotifers, of flatworms, of amphipods and other small 

 Crustacea, and of mollusks ; they are eaten also by the young of 

 numerous species of fishes, by the adults of specialized forms (men- 

 haden, gizzard shad), and by the larvae of batrachians. 



Discussion. — Protozoa, because of their minute size and general 

 inaccessibility to birds, would not be expected to enter largely into 

 the food of this class. The forms eaten by birds are among the best 

 " protected " protozoa, but the possession of shells can hardly be 

 considered as an adaptation for protection from enemies in the case 

 of animals so small as to be easily devoured by almost any carnivorous 

 animals encountering them and which exist in such enormous numbers 

 that vast areas of sea bottom are covered with remains of their 

 shells. In this case as in many others, numbers are so large and re- 

 production so great that the inroads of all enemies are fully dis- 

 counted. Losses to predatory enemies are only a fraction of the total 

 death rate. 



PORIFERA (sponges) 



Many sponges are pervaded by calcareous or silicious spicules 

 which may render them more or less undesirable as food for pre- 

 datory animals. Some are brightly colored and some phosphorescent. 

 " Sponges do not appear to be edible by Fishes or even the higher 

 Crustaceans or Molluscs. Countless lower animal forms, however, 

 burrow in their substance, if not for food, at least for shelter, and 

 the interior of a sponge is frequently found to be teeming with 

 small Crustaceans, Annelids, Molluscs and other Invertebrates." ' 



Sponges have been identified from only 2 stomachs of nearctic 

 birds (Canada goose and lesser scaup) and from their low degree 

 of accessibility to birds, not many cases of feeding upon them would 

 be expected. 



^ Entries under this head for the various groups treated are intended as 

 suggestive rather than as exhaustive. A hst of papers from which nuicli of 

 this information has heen gleaned forms the special bibliograpiiy on pp. 145-201. 

 Notes on the food of reptiles, amphibians, and mammals are mostly from 

 analyses of stomach contents in the Biological Survey. 



^ Parker, T. J., and Haswell, W. A., A te.xt-book of zoology, vol. I, p. 126,. 

 1910. 



