blackman: the spermatogenesis of scolopendra. 77 



tooth-like projections arising from opposite sides of the head, those on 

 one side alternating with those on the other. This appearance is due 

 to the presence of a spiral ridge upon the surface of the head. 



In later stages this spiral continues to become more and more marked, 

 and the head soon appears as represented in Figures 1 1 G — 118. Here 

 the more transparent inner portion is plainly shown, all of the chromatin 

 being arranged at the periphery. A careful study of this stage shows 

 the character of the spiral thickening of the head. In Figure 115 are 

 represented a transverse («) and a longitudinal (/;) section and a surface 

 view (c) of the head at this time. By studying these figures it is at 

 once seen that the spiral represents not only a ridge, but that the crest 

 of the ridge consists of a much thicker deposit of chromatic material than 

 exists elsewhere on the head. This causes the spiral to be even more 

 conspicuous than it otherwise would be. This is very well shown in a 

 study of cross sections of the head (Fig. 115 a). In studying the sec- 

 tions this denser chromatic portion lying upon one side of the head may 

 be seen to shift its position regularly as the microscope is focussed up 

 and down, so that it makes an entire circuit of the cross section. In 

 longitudinal section (Fig. 115 b) the appearance leads to the same con- 

 clusion, for here we get an oblique section of the chromatic thickening. 

 Figure 115c is a reconstruction based on the cross and the longitudinal 

 sections, but the same appearance may be actually seen occasionally 

 where the staining is of exactly the right intensity. 



At the stage shown in Figure 11G the head of the spermatozoon is 

 sometimes compressed in the plane of the two centrosomes, thus forming 

 a ribbon-like structure. This I consider to be due to the loss, at the 

 moment of fixation, of the fluid contained in the central region. It is 

 of great assistance in studying the centrosomes at the base of the head 

 and in obtaining a clear idea of the peripheral disposition of the chro- 

 matin. Figures 117 and 118 represent portions of spermatozoa which 

 have suffered this loss of material and have assumed a ribbon-like form. 

 In both, the two lateral centrosomes are unmistakably evident, as they 

 lie in close apposition at the base of the head. These flattened heads 

 also very often afford an excellent optical section of the entire structure, 

 showing the peripheral band of chromatin upon each side of a central 

 unstained region. In Figure 118 this ribbon-like structure is placed 

 with the flat sides parallel to the plane of the section. In Figure 1 1 7 

 the " ribbon " has been twisted and thus affords optical sections from 

 the edge as well as the side. 



From this time forward, the transformation of the spermatozoon con- 



