26s aquatic microscopy for beginners. 



4. CeriodAphnia. 



The shell is oval, oblong, or somewhat four-sided, 

 and always beautifully, if coarsely and conspicuously, 

 reticulated, the meshes being hexagonal and compara- 

 tively large. The head is separated from the body by 

 a depression in the shelly and just behind the rather 

 small eye-like spot it has a slight elevation. The eye 

 is usually near the rounded lower margin or tip of the 

 beak-like head. The antennae resemble those of 

 Daphnia, being long, and divided into two three- 

 jointed branches of equal length. The angle or tooth 

 on the upper corner of the posterior border is usually 

 sharp and conspicuous. 



This Entomostracan is abundant in the writer's lo- 

 cality. It is visible to the naked eye, being about one- 

 twenty-fifth of an inch long. In the aquarium its 

 movements are almost distinctive. It seems to prefer 

 the center of the vessel, where it darts upward for a 

 short distance with a jerk, only to allow itself to sink 

 back to the starting-point. A glass jar well stocked 

 with these pretty creatures leaping up and down ir- 

 regularly and incessantly is an interesting sight. Un- 

 der the one-inch objective the little animal is more than 

 interesting. 



5. Cypris (Fig. 180)). 



The shell entirely surrounds the animal, so that the 

 little creature, when danger 

 threatens, shuts itself in as com- 

 pletely as a clam or a mussel, 

 and allows itself to fall to the 

 bottom. The form varies from 

 Fig. 180.— Cypris. an Gval to a kidney shape, ac- 



