A Cytological Study of the Semi-parasitic Copepod, Hersilia apodiformis etc. 409 



gonial chromosomes stand out with a clearness and sharpness which re- 

 minds one of Hemipteron preparations. Twenty-eight chromosomes 

 (the diploid number), all with distinct "Querkerbe", can be counted. 



VI. The Growth Period. 

 A. Spermatocytes. 



The growth zone of the testis begins at the bend of the dorsal tube 

 and occupies the greater part of the ventral tube. The cells resulting 

 from the ultimate spermatogonial division mcrease in size, the chromatin 

 remaining in a fine network like that of the quiescent spermatogonia. 

 The paired nucleoli are formed anew and are very conspicuous, as are 

 the cyto-plasmosomes on the nuclear membrane. To illustrate the 

 changes from this stage to that of the bouquet stage and at the same 

 time show the seriation, it was thought best to select a portion of a 

 Single longitudinal section, as represented in Fig. 12 (Plate V). Cells a 

 and b are nearest to the bend of the testis (caudad); cells g and /', nearest 

 the maturation zone (cephalad). A corresponding portion of a testis is 

 shown at a—g in Figure 1 (Plate IV). 



In the formation of the leptotene threads, the first change is a 

 thickening of portions of the fine network of the quiescent nucleus, re- 

 sulting in dark zig-zag threads (Fig. 12, a); and as these chromatin bands 

 become more noticeable (Fig. 12, h), the network between them be- 

 comes less distinct. In the next stage (Fig. 12, c), the leptotene threads 

 can be more easily followed, as they are quite angular and ragged in 

 outline, being composed of dark irregulär granules connected by thinner 

 portions which stain less deeply. The formation of the leptotene threads 

 in Hersilia can not be traced back, as in various Orthoptera (Wilson, '12), 

 to chromatin masses formed from the chromosomes of the ultimate 

 spermatogonial telophase and from which the threads uncoil. 



The next stage (Fig. 12, d) is characterized by the beginning of a 

 polar orientation of the threads, which are now less ragged in outline, 

 although still quite angular. Their free ends point toward one side of 

 the nucleus, generally designated the positive pole. Concomitant with 

 the orientation of the threads are two other phenomena: the approach 

 of the nucleoli toward one another and usually toward the positive pole, 

 and the fusion of the cyto-plasmosomes {cpl.) into two or three of 

 largersize. In Figure 12, e^) we have what may be called the leptotene 



1) The stages represented in Figure 12 d — /' are those most sensitive to the fixing 

 agent, as is shown by a contraction, known generally as synizesis. It is only in the 



