blackman: the spermatogenesis of SCOLOPENDRA. . '• 



is the extremely elongated form of the head and the remarkably largo 

 acrosome. As I have already stated, there is much variation in the 

 size of the cells at all stages after the growth period of the spermatocytes, 

 and this is very noticeable in the spermatozoa as well as at other times. 

 I have represented in Figure 121 what may be regarded as the greatest 

 size. Here the actual length of head and acrosome is 2 GO micra, and 

 of this length the nuclear portion represents 170 micra, while the width 

 of the head is onlv about h micron. It would be interesting to know 

 whether there is any condition existing in the egg of Scolopendra which 

 would require a spermatozoon of such attenuated form. The smaller 

 spermatozoa are of about the same diameter as the large ones, but are 

 much shorter, the heads of some being only about 75 micra in length. It 

 is noticeable that these smaller heads stain more strongly than the larger 

 ones, probably owing to a greater concentration of the chromatin. 



Throughout all the later processes of transformation the lengthening 

 of the cell has proceeded at the same rate as that of the contained struc- 

 tures, and in the fully developed element the entire spermatozoon, — 

 acrosome, head, and flagellum — is surrounded by a rather thick layer of 

 cytoplasm, bounded by a definite membrane (Figs. 120, 121). This is 

 perhaps best shown in cross sections. In those through the head region 

 this layer of cytoplasm occupies at least two thirds of the diameter, 

 which seems to be about the same in all regions of the cell. In the 

 tail region (Fig. 113) the axial filament lies near the centre of the cross 

 section and is surrounded by a layer of dense cytoplasm. 



This study of spermatid changes has- been made exclusively upon sec- 

 tioned material ; while this is undoubtedly very favorable for studying the 

 details of the metamorphosis, it is not so valuable for the study of the 

 general structure of the mature sperm cells as preparations of dissociated 

 material would have been. It is of course practically impossible to 

 obtain a longitudinal section of the entire spermatozoon, owing to its 

 great length and to the fact that it is usually distorted when killed. 

 For this reason I am unable to. give the general topography of the 

 spermatozoon or of the cells in the later stages. I cannot be absolutely 

 certain of the relative length of head and flagellum, but can say with 

 certainty that the latter structure is several times as long as head and 

 acrosome together. Thus the- mature spermatozoa derived from the- 

 larger spermatocytes must reach a length of nearly one millimetre, for 

 the head region is one fourth, this length by actual measurement. 



In Figure 121, which represents a mature spermatozoon as found in 

 the central region of the follicle,, there is quite a thick envelope of cyto- 



