Papers from the Marine Biological Laboratory at Tortugas. 229 



this time, too, the folds that were mentioned before are formed in the second- 

 ary bundles. 



A spermatosome which is in the stage represented by figures 64 and 65 is 

 now ready to undergo the final change which transforms it into the fully 

 formed apyrene spermatozoon (fig. 6). It has been completely filled with 

 the albuminous bodies and all the chromatin has been dissolved in the 

 cytoplasm ; the secondary bundles have come to form folded ridges on both 

 sides of the cell, already indicating the final shape of the undulating mem- 

 branes. The length of the spermatosome, however, exclusive of the flagella 

 is only about 70 micra. A general lengthening and constriction of the cell 

 now take place which result in its becoming spindle-shaped, with an 

 increase of from 15 to 20 micra in its length. At the same time the folds 

 of the secondary bundles are somewhat straightened out and they them- 

 selves become much broader and flatter, assuming the shape and appearance 

 of typical undulating membranes. The fibers are now probably arranged 

 into two outer layers where they are in close juxtaposition to one another, 

 if not actually fused, and a single inner layer where they are more widely 

 separated from each other. The base of the cell is drawn out narrowly to a 

 point, ending with the fused flagella. It is quite possible that the final 

 change in the shape of the cell is to be attributed to the continued growth 

 of the fibers. 



DISCUSSION. 



There are two outstanding differences between the development of the 

 apyrene spermatozoa of Stromhus and that of the oligopyrene spermatozoa 

 of Paludina. The first of these is in regard to their origin. It has been 

 shown by Meves ('03) that the oligopyrene spermatozoa of Paludina arise 

 from the spermatogonia, certain ones of which undergo an unusual growth 

 and become the oligopyrene spermatocytes. In Stromhus the apyrene 

 spermatozoa arise from certain cells which are different from the spermato- 

 gonia and which have been called the apyrene spermatoblasts. Secondly, 

 in their later development, the apyrene spermatozoa of Stromhus do not 

 show nearly as close a parallelism to the development of the eupyrene as 

 do the oligopyrene spermatozoa of Paludina. In both forms the develop- 

 ment of the bundle of axial fibers in the atypical spermatozoon can be 

 closely homologized with the growth of the axial fiber in the true spermato- 

 zoon, but the two divisions of the oligopyrene spermatocyte which take place 

 in Paludina are entirely lacking in the apyrene spermatoblast of Stromhus. 

 Again, in the adult oligopyrene spermatozoon of Paludina the equivalent 

 of one chromosome is retained and forms its nucleus, while the apyrene 

 spermatozoon of Stromhus contains no chromatin at all. Finally, it might 

 be pointed out that the oligopyrene spermatozoon of Paludina shows a much 

 closer approximation to the form of the eupyrene than does the apyrene 

 spermatozoon of Stromhus. 



On the other hand, there exist certain fundamental similarities of 

 development and structure between the atypical spermatozoa of Stromhus 



