SPERMATOGENESIS OF THE BLACK-CLAWED CRAB. 285 



indicated. The second vacuole increases in size and ultimately 

 surrounds completely the central body so that the spermatid 

 presents the picture illustrated by Fig. 55. In this figure the 

 primary and secondary vacuoles have changed into distinct 

 vesicles and from now on they will be designated as the primary 

 and secondary vesicles. 



Soon a thin line grows out from the distal portion of the central 

 body and this penetrates the upper end of the second vesicle to 

 form a small opening (Fig. 56). The central body then begins 

 to hollow out thereby becoming tubular. At the same time the 

 outer opening of the second vesicle becomes collar-like in appear- 

 ance. These changes are seen in Figs. 57-59. Following this 

 the nucleus and mitochondrial ring fuse and become like one 

 structure drawn up tightly around the vesicles (Fig. 60). From 

 this last named nuclear-mitochondrial portion, the radial arms 

 of the mature spermatozoa are formed (Fig. 61). 



The last transformation in the mature spermatozoa occurs in 

 the central body. The proximal end of this structure penetrates 

 the tubular, distal end to form a small spine-like vertical rod 

 (Figs. 62 and 63). This can only be seen in slides of spermatozoa 

 which have been greatly destained. In other slides the sperma- 

 tozoa all present the appearance of the one shown in Fig. 64. 

 When such a male gamete that has been stained with Heiden- 

 hain's hsematoxylin and acid-fuchsin is examined, the central 

 body is uniformly black except for its distal end where it joins 

 the dark collar-like opening, which is clear; the second vesicle 

 is an amber color; the primary vesicle is colorless, and the 

 nuclear-mitochondrial mass is darkly granular, with a darker 

 ring immediately around the second vesicle. Such mature 

 spermatozoa fill in the lower portion of the testis and the vas 

 deferent ducts. 



When these spermatozoa begin to open up one notices that 

 four types of them exist, a three (Fig. 65), four (Fig. 66), five 

 (Fig. 67) and six (Fig. 68) rayed type. The four and five rayed 

 types predominate in largest numbers. The opening up and 

 explosion of these spermatozoa has already been described in a 

 previous contribution to this journal (Fasten, '21). As pointed 

 out in that paper, the explosion is produced by a lowering in 

 the osmotic pressure of the medium which surrounds the gametes. 



