33O D. D. WHITNEY. 



more careful observations were made both upon such living cells 

 and upon stained ones it was readily seen that these cells were 

 not immature stages but were the mature stages of the sper- 

 matozoa. The heads are quite large in proportion to the diameter 

 of the tail, Fig. I, B, and are easily separated from the tails. 

 In the testis of the male these spermatozoa are in clusters and 

 in each cluster each spermatozoon is attached to some sort of a 

 central tissue in the cluster. Normally in copulation with the 

 young females a few of these spermatozoa become detached from 

 the central tissue and are extruded into the body cavity of the 

 female. When, however, the males are crushed under a cover 

 glass nearly every head remains attached to this central tissue 

 but the tails break off from the heads and are immediately ex- 

 truded in a writhing mass. If the males are sufficiently crushed 

 the mass of spermatozoa heads will also be extruded together 

 with other cells of the broken-down tissues. If very young 

 males are taken from the eggs and are crushed all of the immature 

 sperm cells with the tails attached will be extruded. The ripe 

 spermatozoa resemble very closely these immature spermatozoa 

 except their heads are more rounded and the tails are somewhat 

 longer. 



The males of another rotifer, Hydatina senta, were crushed 

 and the spermatozoa reexamined. A few males shed both kinds 

 of spermatozoa with the tails attached to the heads. These 

 were stained and the heads of each kind were found to contain 

 chromatin material similar to the heads of the spermatozoa of 

 Brachionus mulleri. These are shown in Fig. 3. Twenty-five 

 males were crushed and out of the many hundred spermatozoa 

 ejected only about 6-8 entire spermatozoa of each kind with 

 the tail attached to the head were found. Hydatina senta 

 males are the most favorable material thus far examined in which 

 to see the two kinds of complete spermatozoa in a mature male. 

 In Brachionus mulleri these two kinds of complete spermatozoa 

 could only be found in the unhatched and immature males. 



The spermatozoa were examined from mature males of two 

 additional species of rotifers, Brachionus amphiceros, and Dias- 

 chiza sterea. The entire normal spermatozoa with the tails 

 attached to the heads were found in each species. Upon staining 



