466 M. Louise :N'iehols. 



Tlu' i'(MliK'ti<»ii ill size and especially in length of the spermatid in 

 the course of its development is very marked. (PI. 3. Hi, 29-34.) 

 Its apearance as sliouni in Figs. 27-29 brings to mind the matnre 

 spermatozoon of -Ilomarns, except of course for the greater relative 

 size of the head. It is possible that there is here recapitnlated a 

 stage in the phylogeny of the spermatozoon of Hippa. 



The spermatid goes throngh a remarkable series of transformations 

 during its development. The chromatin in the nuclei of the young 

 spermatids is arranged in bands forming a coarse meshwork with 

 large interspaces. (Fig. Hi, 22.) The cytoplasm, at first uniform, 

 soon shows a dense ring around the nucleus. The remainder of the 

 cytoplasm loses the appearance of a network and no longer stains 

 with iron hsematoxylin. (Fig. Hi, 24.) Koltzoif, in his beautiful 

 Figs. 1-3, PI, XVI, shows the origin of this diiferentiation of the 

 cytoplasm in the accumulation and segregation of corpuscles differ- 

 ing from each other in size and in staining capacity, to both of 

 which he gives the name mitochondria. The smaller and darker 

 granules form a mass adjoining the nucleus and correspond to the 

 ring just described for Hippa. They are destined to form the middle- 

 piece of the mature spermatozoon, while the larger and lighter cor- 

 puscles coalesce to form the tail capsule. The fixation employed 

 for Hippa does not serve to bring out these granules, but the differ- 

 entiation of the cytoplasm is clear. In rare instances the miTochoii- 

 di-ial body may lie side by side wnth the nucleus within the cell 

 (Fig. Hi, 23), but in general its appearance is that of Fig. Hi, 24. 



Within the mitochondrial body and at one side of the nucleus 

 arise thickened strands which extend to the periphery of the cell. 

 They will become the streamers or projections from the middle-piece 

 of the mature spermatozoon. As the ring increases in diameter and 

 decreases in thickness the strands are gradually more uniformly dis- 

 tributed and no longer appear to arise from so circumscribed an 

 area. (Fig. Hi, 25.) At the same time the nucleus has increased 

 to about twice its former size, the bands of chromatin have nearly 

 disappeared and the entire nucleus stains much more faintly. 



The tail capsule has taken a more definite shape, but remains 

 unstained. (Fig. Hi, 25a.) It next commences to elongate, a cavity 



