150 



I. IKE DA. 



when the entire vascular wall is covered by the loosend strings up to 

 the blind end. 



Pl. V., fig. 5 shows a cross-section of a fully developed and 

 functional testicular capillary. (In the capillary lumen is seen a blood- 

 corpuscle). It will be observed that the spermatogonia lining the testicu- 

 lar strings are very small in siz3 and approximately spherical in shape. 

 They contain a comparatively large and vesicular nucleus in which are 

 visible a few number of dot-like chromatin. Towards the outer end of 

 the strings they grow somewhat larger while the chromatin dots in the 

 nucleus become more numerous and distinct. The largest cells at the 

 outermost end may be called the spermatocytes. They are more or less 

 detached from connection with the strings and are loosely adhering to 

 one another in the periphery of the testicular capillary. Here the divi- 

 sion of the spermatocytes into spermatids and the development of these 

 into spermatozoa may without difficulty be studied. 



In figs. 5 and G, the same lettering has been used to denote the 

 same stages in the spermatogenesis. The cell indicated by a is a loosely 

 lying spermatocyte, in which the chromatin has the form of a spiral 

 hand (spireme). The cell b is another in a more advanced spireme stage. 

 Soon the nuclear membrane dissolves away and the karyokinetic figure 

 distinctly establishes itself. The rod-like chromosomes, in the equator- 

 ial plane of the spindle, number six in P. ijimai and twelve in 

 P. aus traits. In c and d the karyokinesis is progressing ; the division 

 ensues, which is directly followed with another without the nucleus 

 passing through a resting phase. The letter e indicates the daughter 

 cell produced by the first division of a spermatocyte and /, one of the 

 four spermatids given rise to by it after the second division. The sper- 

 matid is very small, corresponding in bulk to about one-fourth of the 

 original spermatocyte. Only half the normal number the chromosomes 

 enters into it, exactly as in a ripe ovum. Tints, in P. ijimai their num- 

 ber to each spermatid is three, which are at first so attached to one 

 another with their ends as to present a triradiate figure (see fig. 5, /). 

 This is soon followed by a stage in which the spermatid is supplied with 



