330 BULLETIN: MUSEUM OF COMPAEATIVE ZOOLOGY. 



in size, reaching its maximum in the stage shown in Figure 93, where its 

 bulk is more than doubled. The chromatic net, at the same time, be- 

 comes much looser, lying close against the sharply denned nuclear 

 membrane, leaving the central portion of the nucleus unoccupied. Con- 

 densation appearances, so characteristic of the spermatocytes, do not 

 occur in the spermatids, probably owing to their small size. After attain- 

 ing its maximum size (2.5 p) the nucleus diminishes once more. The 

 chromatin becomes condensed in certain areas, losing its definite net-like 

 arrangement, and frequently exhibits the appearance shown in Figure 96, 

 where it forms two distinct masses near the poles, connected by an axial 

 rod. With further decrease in the size of the nucleus, the chromatin 

 becomes diffused evenly throughout it, so that the entire nucleus takes 

 a dark stain. The basal chromatic mass appears, however, to persist, 

 although of this I cannot be certain ; it is probable that we must inter- 

 pret as such the deeply stained plate which forms the base of the conical 

 head in the adult spermatozoon (Fig. 102). At its maximum size the sper- 

 matid nucleus attains a diameter of 2.5 fi, but diminishes to about 2 p. 

 The chromatin, from the time when it becomes diffused throughout the 

 nucleus, undergoes an important change in its staining reaction, for when 

 treated with the gentian-safranin mixture, so useful in the study of 

 spermatid metamorphosis, it takes the safranin dye as strongly as it 

 previously did the gentian. This reaction is very helpful, since it 

 strongly emphasizes the line of separation between the nucleus on the 

 one hand and the archoplasmic structures and the acrosome on the other, 

 both of the latter staining blue. The nucleus now becomes flattened 

 on the side toward the tail filament, where it is bounded by a more 

 deeply staining chromatic plate, and gradually changes as a whole from 

 a spheroidal to a broadly conical form (Fig. 99). Seen in polar view it 

 is circular (Fig. 100) and surrounded by a layer of cytoplasm. Mean- 

 while the proximal centrosome becomes more and more intimately con- 

 nected with the nuclear substance, until finally it can no longer be 

 demonstrated as a separate body, although represented by a minute 

 prominence long visible at the point of fusion (Fig. 101). There is, 

 however, in Gonionemus no direct evidence that this centrosome actually 

 penetrates into the nucleus, I believe, therefore, that it merely becomes 

 flattened against the basal portion of the nucleus, being obscured from 

 view by the deeply staining pi-operty of the latter. 



While these changes have been taking place, further modifications 

 occur in the archoplasmic organ. This, when the nucleus was largest, 

 consisted of two small masses at the base of the nucleus, which, with 



