322 EDWIN E. REINKE. 



that the tail-piece breaks off and the spermatozoon swims a way 

 with a much more rapid movement than it had at first. When 

 the tail-piece begins to break off it can be seen to be composed 

 of a number of fused flagella; sometimes as the spermatozoon 

 moves away one or more of the flagella may be seen still adhering 

 to it. This explains the statement of Brock to the effect that a 

 tuft of flagella, which is invisible at first, is to be seen after the 

 spermatozoon has been swimming about for a while. It very 

 frequently happens that long before the undulations of the mem- 

 branes have ceased, the spermatozoon flattens out and the 

 albuminous bodies break down, leaving in their place a brownish, 

 semi-fluid substance in which, however, may still be seen the 

 outlines of those bodies. 



As in Pahidina, the apyrene spermatocytes of Strombus are 

 easily recognized. They are large pear-shaped cells provided 

 with a nucleus of regular pattern and a large centrosome about 

 which may be seen an inner clear court and an outer dark court. 

 Until a very late stage in their growth period they retain a con- 

 nection with the cyst-wall of the testis by means of a short stalk; 

 later they lose this attachment and become spherical. By this 

 time the chromatin has begun to form in lumps beneath the 

 nuclear membrane and from a large number of centrioles lying 

 at the periphery of the centrosome strong radiations may be 

 seen to pass out in all directions (Fig. 6). In the outer court, 

 but away from the nucleus, lies a mass of mitochondria. A divi- 

 sion of the nucleus and cell never follows; instead, the nuclear 

 wall breaks down and the centrosome with its radiations dis- 

 appears. A little later the chromatic masses are seen scattered 

 through the cell while the centrioles have moved to the periphery 

 of one half of the cell where they are easily recognized by their 

 radiations (Fig. 7). The cell now begins to develop directly into 

 the spermatozoon. 



The chromatin, as such, takes no further active part in the 

 development of the spermatozoon; the fragments very soon 

 begin to become vesiculated and to degenerate. The centrioles 

 mass together at a point just beneath the cell membrane where 

 they divide (Fig. 8). One half of the number of daughter or 

 secondarv centrioles remain attached to the cell-membrane and 



