rtt? 



7b BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



much decreased, and its form becomes more definite and regular (Figs. 

 L05, 106). I think it probable that the increased intensity of the stain- 

 ing is due to the condensation of the acrosome material rather than to 

 the absorption of material from the nucleus. It is the peripheral portion 

 only that is stained, the material within the cavity of the vesicle remain- 

 ing entirely transparent. 



The acrosome retains the pear or club shape for a considerable time 

 (Figs. 105, 106), but when the nucleus begins its second period of 

 lengthening (Fig. 109) the acrosome also undergoes a similar change. 

 The first stages in this process are rather peculiar. One would naturally 

 expect the vesicle merely to elongate through its whole length, but such 

 is not the case. A protuberance appears upon one side of the acrosome 

 near the anterior end ; this gradually extends farther and farther for- 

 ward, giving it the peculiar appearance shown in Figure 109. As the 

 process continues to elongate, the contour becomes more regular and the 

 acrosome soon assumes the form of a thick filament, which tapers slightly 

 toward the anterior end, but does not terminate in a sharp point (Figs. 

 110, 111). From this stage the elongation continues until, in the mature 

 spermatozoon, the acrosome is a slender filament sometimes nearly 

 100 micra in length and correspondingly slender, its greatest diameter 

 being rather less than 2 micra. The proximal end is blunt or rounded 

 and is connected directly with the anterior end of the head (Fig. 121). 

 The distal or anterior part of the acrosome tapers very gradually and 

 ends in a sharp point (Fig. 121). No barbules, such as are of frequent 

 occurrence in other animals, have been observed. 



After the stage represented in Figure 109 the head of the young sper- 

 matozoon elongates rapidly and soon has the form shown in Figure 110. 

 At this time numerous small vacuoles are in some cases to be seen in 

 all parts of the head (Fig. Ill), while in other cells there are one or 

 two large vacuoles, which occupy nearly the entire central portion (Fig. 

 112). Cross-sections of spermatozoa in this condition are shown in 

 Figure 113, where the diameter of the chromatic sheath is about one 

 fourth that of the entire head. This vacuolation continues to become 

 more marked, and as the vacuoles unite a larger and larger one is formed, 

 which in the mature spermatozoon occupies the entire central region and 

 extends the whole length of the head (Figs. 116-121). 



As the elongation continues, the anterior end of the head becomes 

 tapering (Fig. 114). At about the same time the first indications of a 

 spiral condition are to be observed. This condition is first apparent 

 near the base, and in longitudinal section it presents the appearance of 



