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FRESH-WATER BIOLOGY 



internal and external; in meeting and solving the problems which 

 the world presents. And it is almost surprising to note, when the 

 matter is first examined from such a standpoint, how nearly the 

 objects of the strivings of almost any lower group resemble those 

 of the highest. To get proper food and oxygen; to find or construct 

 a proper place to dwell; to arrange for the production and growth 

 of the young; to protect one's self and one's progeny from ene- 



FlG. 8s7. Notommatoid rotifers. A , Notommata Iruncata Jennings, side view. X 300. B, same, dorsal 

 view. X 300. C, Copeus pachyurus Gosse. X 150. The letters in Figs. 856 and 857 have the follow- 

 ing signification : 6r, brain; c, cloaca: co, copulatory organ; ct, contractile vacuole; e, eye; ea:, excretory 

 organs; /, foot; /c, flame cell; gg, gastric glands; in, intestine; la, lateral antennae; m, mouth; mg, 

 mucous glands of foot; ms, muscles; mx, mastax; 0, esophagus; ov, ovary; sg, salivary glands; sp, 

 spermarium; st, stomach; t, toes. (After Weber.) 



mies and from the forces of nature, — these, and the activities 

 growing out of them, form the groundwork of life in the lowest as 

 well as the highest creatures. In studying the rotifers, it will be 

 best to look upon them as hving things and to ask: What processes 

 and activities are they carrying on? And what apparatus do they 

 use in these activities? Thus, one is led to take up in order the 



