ANATOMY AND METAMORPHOSIS OF CYCLOPS. 223 



it quiet, examine the basal joints of the antennules with 

 the highest magnifying power that can be used (fi'om fifty 

 to one hundred diameters). Notice the thin-walled, trans- 

 parent \ esicle, the otoc^'st, which nearly fills the enlarged 

 basal joint of the antennule. On the upper surface of the 

 antennule notice the ti^ansverse slit through which the oto- 

 cyst opens to the exterior. Xotice the row of hooked 

 hairs which project over this slit, as a sort of thatch. In 

 the cavity of the otocyst a number of small gi-ains of sand. 

 A row of long, slender, sensory hairs, Avhich project from 

 the wall of the otoc^'st into its cavity, on the side nearest 

 the median line of the body. On the posterior or basal 

 side an irregular cluster of shorter hairs. 



An examination of the hearing organ of the adult crab, 

 and of the lobster or crayfish, will show that the megalops 

 larva differs from the adult and resembles the lobster, in 

 having the otocyst open to the exteriq^. The grains of 

 sand also are present in the otocysts of the lobster, but 

 absent in that of the adult crab. 



,:XXII.— THE ANATOMY AND 3IETAM0RPH0SIS OF 



CYCLOPS. 



Small Copepods are usually abundant in both fresh and 

 Isalt water, and there is never any difficulty in obtaining 

 tthem. As Cyclops is one of the most common and widely 

 lifiused fresh- water genera it has been selected for de- 

 3ription, but there should be no difficulty in studying other 

 forms, for although the generic differences are very con- 

 siderable, they are not of such a character as to confuse 

 the student. In order to obtain a supply of specimens of 

 .y clops, carefully examine the sides of an aquanum in 

 rhich water plants have been growing, and search for 



