i88 



EIGHTEENTH LECTURE. 



at p. 14 may, indeed, commence without spermatozoa, and 

 even in the mammalial animal ; but it soon ceases. When, 

 however, the seminal elements have mingled their expiring 

 body with the yolk, then (in an enigmatical manner, it is 

 true), the multiplying process of the segmentation of the vi- 

 tellus is continued, until at last innumerable building stones 

 have been acquired, of which we have already spoken (p. 179). 

 Whence comes the seminal filament ? 



For more than one generation this question has been very 

 correctly answered : from the convoluted canals of the testi- 

 cle. But the hozv has called forth the most diversified an- 

 swers among the older investigators, their successors, as well 

 as the present generation of histologists. The incipient, 

 crude and bad methods of examination certainly led the pio- 

 neers to the grossest delusions. 



That we at present understand the whole, I certainly doubt 

 very much ; still we have made some progress. 



Let us listen, therefore, to the results of the most recent 

 studies (Neumann, von Ebner, Mihalkovics). 



We have already mentioned (p. 185) that the most external 

 gland-cell layer of the quiescent seminiferous canal presents 



a prismatic radiated form. This 

 cell is the spermatozoa-producing 

 structure. All the numerous inner 

 cells of this glandular canal appear 

 to have no future ; they form merely 

 an indifferent redundant substance. 

 When the seminal gland becomes 

 active — in mammals this is only pe- 

 riodically the case, generally once 

 a year, in man in uninterrupted se- 

 quence throughout the entire pro- 

 creative epoch — when, therefore, 

 the testicle is active, a remarkable 

 metamorphosis occurs in these pris- 

 matic parietal cells (Fig. 165, b). 

 The epithelial cell-body grows inwards, that is towards the 



Fig. 165. — From the seminiferous 

 canals of the rat ; «, parietes with the 

 cell nuclei ; parietal cells and sperma- 

 toblasts , c, the latter with small nar- 

 row nuclear corpuscles ; d, inner cell 

 layer. 



