764 EEPOET OF COMMISSIONER OF FISH AND FISHERIES. [10] 



we not sbowu that on the fronds of tliese algse there exists, in most 

 instances, almost a forest of protozoan life upon which these creatures 

 may be supposed to pasture ? We do not find the Laminaria itself 

 eaten. Again, the foraminiferal and radiolarianfaunaof the high seas 

 appears to be in great measure, a surface fauna, according to the evi- 

 dence of a number of investigators. This fact appears to have an im- 

 portant relation to the vast shoals of Copepoda observed at the surface 

 of the sea by various naturalists and expeditions. It is not to be sup- 

 posed, however, from what has been said, that the Copepoda are the 

 only consumers of this vast array of individual Protozoa. Cross sec- 

 tions through the oyster, which the writer has i^repared and mounted, 

 show the tests of various genera and species of diatoms mixed among 

 the indigestible earthy matters and sediment which has been swallowed 

 along with the food. It is probable that the oyster swallows and digests 

 manj" of its own embryos, and not improbably many embryos of such 

 forms as Bryozoa and Sponges, besides the Diatoms, Desmids, and Pro- 

 tozoa which make up the most of its food. Ordinarily the contents of 

 the stomach of the oyster are too much disorganized to learn much 

 about what it has recently swallowed, hence we are at a great loss to 

 know just exactly of what all of its food consists. Just so with the 

 Copepoda 5 they themselves are doubtless eaten by other Crustacea, 

 these in turn by others. We saw that Doris and ^olis i)astured upon 

 the forests of fixed Protozoa, just as Planorhis, Lymnaeus, and Physa 

 pasture upon the Protozoa, Algse, Diatoms, and Desmids, in fresh 

 water. The great abundance of Copepoda and Amphipoda is, however, 

 the best evidence of the abundance ofstill smaller forms adapted to furn- 

 ish them with food. What multitudes of forms besides Copepoda must 

 largely subsist upon the Protozoa and Protophytes? Of such groups 

 we may name the Lamellibranchs, Pteropods, Worms, Bryozoa, Por- 

 ifera, and, doubtless, many Ccelenterata. Some of these, notably the 

 Lamellibranchs, could i)robably not exist were it not for the numerous 

 Protozoa and Protophytes, ui)on which, from necessity, they are com- 

 pelled to feed. 



What is true of the fauna of the sea appears to be in an equally great 

 measure true of the faunae of fresh water ponds, lakes, and streams. 

 Eecently I investigated some Daphniadce v/hich had been kept for some 

 time in an aquarium ; to my surprise I did not find any recognizable re- 

 mains of animal food in the intestines. The latter were, however, entirely 

 filled with a sarcode-like material, doubtless in part a digestive secre- 

 tion, together with what might have in part been animal food. The 

 vegetable food, consisting of Diatoms, unicellular Algse, spores of Fungi, 

 fragments of Oscillatorice, were so sparingly mixed with the intestinal 

 contents that they could not be regarded as contributing much to the 

 nutrition of the animal. The black or brown material, sometimes filling 

 the intestine of Entomostraca, I find to consist in great part of humus, 

 particles of quartz sand and earthy matters, which are of course indi- 



