SPERM ATOGENESIS. 377 



presents throughout a nearly homogeneous structure. This sub- 

 stance is first noticed in the spermatocytes, disappears during the 

 cell-divisions resulting in the spermatids, and reappears in the latter. 

 In the protoplasm of the spermatid, lying near the nucleus, there 

 is further found a small globular body, the chromatoid accessory 

 nucleus of Benda, smaller than the sphere and staining very deeply 

 in Heidenhain's hematoxylin. A true centrosome may also be 

 found in the spermatid. 



The nucleus of the spermatid develops into the head of the 

 spermatosome, during which change the originally spheric nucleus 

 becomes somewhat flattened and at the same time assumes a denser 

 structure and moves toward that portion of the spermatid pointing 

 away from the lumen of the seminiferous tubule. Accompanying 

 these changes in the nucleus, marked changes are observed in the 

 shape and structure of the sphere, which marks the position of the 

 future anterior end of the head of the spermatosome, and applies 

 itself to the nucleus on the side pointing away from the lumen of 

 the tubule. In this position it differentiates into an outer clear 

 homogeneous zone and a central portrn which stains more deeply 

 and to which v. Lenhossek has given the name akrosome. From 

 these structures are developed the head-cap and the lance of the 

 spermatosomes, which differ in shape and relative size in the sper- 

 matosomes of the different vertebrates. Recent investigation seems 

 to establish quite clearly that the axial thread of the tail is devel- 

 oped from the centrosome (from the larger, if two are present), which 

 is situated at some distance from the nucleus. Soon after the begin- 

 ning of the development of the axial thread the centrosome wanders 

 to the posterior part of the future head of the spermatosome (the 

 pole of the nucleus opposite the head-cap) and becomes firmly 

 attached to the nuclear membrane in this position (observations 

 made on the rat by v. Lenhossek, and on the salamander by Meves). 

 The middle piece and the undulating membrane, it would appear, 

 are differentiated from the protoplasm, although the question of the 

 mode of their development is still open to discussion. The chro- 

 matoid body assumes a position near the axial thread at its junc- 

 tion with the cell membrane ; its fate has not, however, been fully 

 determined. 



According to Hermann (97), the end-piece in the selachia is 

 derived from the centrosome, the ring-shaped body from the invagi- 

 nated half of the intermediate body of the spermatid fornfced during 

 the last spermatocytic division, and the axial thread from filaments of 

 the proximal half of the central spindle. The lance, according to 

 him, represents a modified portion of the nuclear membrane of the 

 spermatid. 



For further particulars regarding spermatogenesis see the in- 

 vestigations of v. la Valette St. George, 67-87 ; v. Brunn, 84 ; 

 Biondi, Benda, Meves, and v. Lenhossek. 



