Papers from the Marine Biological Laboratory at Tortugas. 219 



through a cell of approximately the same age as the preceding one. This 

 cell and others similar to it present the appearance of having polyasters 

 on its one side, while on the other lies the majority of the now vesiculated 

 karyomerites. 



This appearance is not maintained for any length of time, for the 

 centrioles, with the lengthening of their rays, draw together and form a 

 somewhat oval plate just beneath the membrane (fig. 33). The flagella 

 now form a short, thick brush on the outside of the cell. The rays which 

 have now grown very strong, traverse the cell for a short distance as a 

 compact column and then, diverging, they extend to all parts of the cell. 

 A little later the centrioles divide and then the distal halves begin to move 

 across the cell, forming fibers between themselves and the proximal halves. 

 The latter, which are perhaps smaller than the others, flatten themselves 

 against the membrane, each one forming a node at the base of its flagellum. 



The mitochondria can now be seen lying above the centrioles and encir- 

 cling the rays which pass off from them. This irregular ring of granules 

 is shown in cross-section in figures 33 and 35 and in surface view in figure 34. 

 After the dissolution of the nuclear membrane and the dispersal of the 

 karyomerites the mitochondria become obscured for a time, owing to the 

 great difficulty of distinguishing between them and the smaller chromatic 

 elements. They apparently remain in much the same position they occu- 

 pied before the dissolution of the centrosome. With the vesiculation of the 

 karyomerites they can once again be distinguished, but they now appear 

 much more irregular in outline and size (figs. 28 and 29). Later they form 

 the ring mentioned above. 



The spermatoblast has now reached a condition in which it is ready to 

 undergo the growth and differentiations which lead directly to the forma- 

 tion of the adult apyrene spermatozoon. With the completion of the pri- 

 mary growth of the cell, the nucleus has broken down to form a number of 

 small chromatic vesicles. As will be shown later, these are concerned 

 with the secondary growth of the cell, after which their degeneration sets in. 

 By the accumulation of the centrioles at one point of the cell, and their 

 subsequent division, the orientation of the matured apyrene spermatozoon 

 is established; for, as has been pointed out, the antero-posterior axis of 

 the spermatozoon is determined by the direction in which the distal halves 

 of the centrioles traverse the cell. For these reasons the cell may now be 

 spoken of as the apyrene spermatosome. 



Before proceeding with the description of the growth and differentiation 

 of the spermatosome, two facts must be considered concerning the spermato- 

 blast : The first has to do with the polarity of the cell and the second with 

 the lack of a strict time correlation between the breaking down of the 

 nucleus and the disappearance of the centrosome, and between the phe- 

 nomena immediately subsequent to both. 



It has already been explained that the orientation of the apyrene sper- 

 matozoon is a morphological one, based upon the direction of growth of 



