142 J. DUESBERG 



the head becomes somewhat elongated and the branches of the 

 horse-shoe are by the same process brought nearer together (fig. 

 16, 17 and 18). At the same time the head loses its symmetry 

 inasmuch as it becomes somewhat curved along its antero-pos- 

 terior axis and its posterior facet becomes oblique, instead of 

 being perpendicular, to the same axis. From this time on we 

 can distinguish what I have, arbitrarily of course, termed 

 face- views (figs. 16 and 21) and side-views (figs. 17, 18 and 20) 

 of the spermatozoon. 



All the modifications of the head are more easily followed on 

 acid fuchsin-methylgreen preparations than on Benda's, for 

 methylgreen gives a sharper stain for chromatin than sodium- 

 sulfalizarinate. In material fixed with Regaud's fluid the clear 

 middle-space of the head appears very conspicuous even in the 

 last stages; but curiously enough, as soon as the spermatozoa 

 have reached the excretory ducts, the staining reaction changes 

 and the head takes up acid fuchsin instead of methylgreen. In 

 preparations made from material fixed with Benda's fluid the 

 ripe spermatozoa, that is, those which have reached the excre- 

 tory ducts, appear somewhat different from those fixed in Re- 

 gaud's fluid. In a side-view (fig. 20) the clear middle-space ap- 

 pears only indistinctly. In face- views (fig. 21) on the other hand, 

 the same space is very conspicuous and sharply delimited, and 

 has the appearance of a canal running from the posterior to the 

 anterior extremity of the head. 



During this period changes take place in the mitochondria 

 also. Their number decreases and their size increases: in other 

 words, there is a fusion of granules. This process can be best 

 followed in Regaud's preparations for the reason that the thin 

 sheet of protoplasm which keeps the mitochondria in place (figs. 

 14 and 15) and which is hardly visible in Benda's preparations, 

 swells in Regaud's fluid as do also the mitochondria themselves. 

 Consequently, the cells and the granules are somewhat larger 

 than in Benda's preparations and they are more scattered. 

 These differences are well illustrated by figures 15 and 19, which 

 represent approximately the same stage, after Regaud's and 

 Benda's fixation respectively. Thus in figure 15 we can count 



