756 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [2] 



sume large numbers of these Protozoans where the surface of the ooze 

 of the bottoms of the streams and pools inhabited by the fishes was 

 favorable to the propagation and healthy existence of the former. 



In order to render the vast multitude of Protozoa available as fish- 

 food it is necessary that they be consumed by larger organisms, which 

 in their turn may be consumed by the fishes. Upon investigating the 

 literature relating to the food of the smaller crustaceans, especially of 

 the Bntomostraca, which enters so largely into the food supplies of most 

 young fishes and very many adult forms, I find that the almost unani- 

 mous testimony of various observers is to the effect that these creatures 

 are largely carnivorous, and subsist mostly upon Protozoa, or the low- 

 est grade of animal existence. In ])roof of the foregoing the following 

 extracts are here introduced. 



In his Natural History of the British Entomostraca, page 6 of the 

 introduction. Dr. W. Baird remarks : " I have no doubt that most of the 

 Entomostraca are essentially carnivorous, and 1 have frequently seen 

 specimens of Cypris hi their turn, as soon as dead, attacked immediately 

 by quantities of Cyclops quadricornis, which in a few minutes had fast- 

 tened themselves upon the dead animal, and were so intent upon their 

 ])rey that they were scarcely frightened away from it by being touched 

 with a brush. In a short time the Cypris might be seen lying at the 

 bottom of the vessel, the valves of the shell separated and emptied of 

 its contents. Leeuwenhoek and De Geer not only maintain that the 

 Cyclops quadricornis lives upon animalcules, but that it even preys upon 

 its own young, a fact which I have also noticed myself. Jurine asserts 

 that the Cyclops quadricornis is carnivorous from taste, and only her- 

 bivorous from necessity ; while the Daphnia puJex he distinctly affirms 

 lives upon animalcules. Place a few Entomostraca, such, for example, 

 as the Daphnice, Chirocephali, Lyncei. etc., in a vessel with j)ure, (;lear 

 water and only some vegetable matters in it, and they gradually be- 

 come languid, transparent, and finally die; but mix with this water 

 some which contains numerous Infusoria, and the Entomostraca will 

 then be seen speedily to assume another aspect. They become lively 

 and active, and the opacity of their alimentary canal testifies sufficiently 

 the cause of it. When, indeed, we consider the amazing quantity of 

 animals which swarm in our ponds and ditches, and the deterioration of 

 the surrounding atmosphere which might ensue from the putrefiiction 

 of their dead bodies, we see a decided fitness in these Entomostraca 

 being carnivorous, thus helping to prevent the noxious effects of putrid 

 air which might otherwise ensue ; whilst they in their turn become a 

 prey to other animals which, no doubt, serve their purposes also in the 

 economy of nature." 



" The food of the Lynceidce,^^ says Baird, " consists of both animal 

 and vegetable matter, and while they prey upon animalcules smaller 

 than themselves they in their turn are devoured in great numbers by 

 insects larger than they are." 



