20 EMBRYOLOGY. 



The spermatozoa have often been designated and it seems 

 to us with entire justice as ciliate, or still better as flagellate, 

 cells. 



The spermatozoa of the remaining Vertebrates have a similar 

 structure to that of Man ; on the whole, the diversity of form which 

 is encountered in the comparative study of the egg-cell in the animal 

 kingdom is wanting here. 



That spermatozoa are in reality metamorphosed cells cannot be 

 more clearly demonstrated than by their development. According 

 to the extended observations of LA VALETTE and others, each 

 spermatozoon is formed from a single seminal cell or spei matid, and, 

 to be more precise, the head w formed from the nucleus, the contractile 

 filament from the protoplasm,. 



The metamorphoses which take place in the development have 

 been investigated with the greatest detail by FLEMMING and 

 HERMANN in the case of Salamandra maculata, the spermatozoa of 

 which are characterised by their very great size. The individual 

 spermatozoon here consists of: (1) a very long head, which has the 

 form of a finely pointed skewer, and takes up stains with avidity ; 

 (2) a short cylindrical middle piece, which differs from the first part 

 in chemical properties also ; (3) the motile caudal filament, which in 

 the Salamander exhibits the additional peculiarity that it is provided 

 with a contractile undulating membrane. Of these three regions 

 the skewer-like head, and probably also the middle piece, arise from 

 the nucleus of the spermatid, whereas the contractile filament is 

 differentiated out of the protoplasm. In the development of the- 

 head the nucleus of the seminal cell is seen to become more and 

 nore elongated (fig. 10 A, B); at first it takes the form of a pear 

 \fig. 10 A k) ; then it grows out into an elongated cone (fig. 10 B A;), 

 the base of which serves as the point of attachment for the middle 

 piece (mst). The cone becomes elongated and narrowed into a rod 

 (fig. 11-4, ), which is finally converted into the characteristic form 

 of a skewer. With this elongation of the nucleus the chromatic 

 network becomes more and more dense, and at last assumes a quite- 

 compact and homogeneous condition, as in the mature spermatozoon. 

 The fundament (Anlage) of the middle piece (figs. 10, 11, A, B, mst} 

 makes its appearance early when the nucleus begins to elongate 

 at that end of the nucleus which was called its base, in the form of 

 a small oval body, which at first takes up stains like the head, but 

 afterwards loses this proper' ty. Its first appearance demands still 

 further elucidation. 



