XII.-THE PROTOZOA AND PROTOPHYTES CONSIDERED AS THE 

 PRIMARY OR INDIRECT SOURCE OF THE FOOD OF FISHES.* 



By John A. Ryder. 



In the course of observations made during the last few years the 

 writer has been more and more impressed with the importance of the 

 Protozoa and Protophytes as an indirect or primary source of much of 

 the food consumed by man. This is notably true of what is known as 

 fish and shell-fish food. As very striking instances of the truth of these 

 propositions we need only to allude to the various edible species of 

 the herring family, the shad, herring, and sardine, the gill-rakers of 

 which are modified so as to enable them to strain the minute living or 

 ganisms out of the water which is passed through the mouth in respi- 

 ration; the menhaden or J5revoor ^ia, which is of the same family and 

 swarms along our coast, and which in its turn furnishes a large propor- 

 tion of its food to the edible bluefish, and so serves this tyrant of the 

 sea as a strainer, elaborator, and accumulator, as it were, of the minuter 

 life of the oceanic wastes which it inhabits. The oyster, in like manner, 

 subsisting as it does entirely upon Protozoa, Diatoms, minute ciliiited 

 larvae, &c., reminds us forcibly that for some of the most savory luxu- 

 ries of the table we are indirectly indebted to the existence of countless 

 hosts of living marine beings which can be rendered visible only with 

 the help of a microscope. 



Comparatively few fishes appear to be able to utilize the Protozoa 

 directly as a source of food. The most remarkable exception to this 

 rule was first made known by Professor S. A. Forbes, of Illinois, who 

 found the intestines of certain young suckers or Gatostomidce packed 

 with the shells or tests of Difflugian Khizopods. In the Proceedings of 

 the Academy of Natural Sciences of Philadelphia for 1881, Professor 

 Leidy states that upon examining two slides containing some of the 

 intestinal contents of young Myxostoma macrolepidotum and Erimyzon 

 sucetia submitted to him for examination by Professor Forbes he was 

 able to distinguish the shells of six distinct species of Ehizopods or test- 

 covered Amoeboid Protozoa. The habits of the fishes in question are, 

 however, mud-loving, and since they are provided with a more or less 

 suctorial mouth it is easy to understand how they might readily coa- 



* Second edition, revised. 

 [1]' 755 



