SPEfeMATOGENESIS OF STENOBOTHRUS VIRIDULUS. 



11 



become more and more ragged ; and this dissociation of chromatin continues 

 until we see again the characteristic resting-stage with its chromatin 

 granules disposed along linin threads, which combine either in reality or in 

 appearance to produce a complete reticulum. The whole process is merely 

 an inverse repetition of that preceding division. The heterotropic chromosome 

 takes no part in this diffusion of chromatin, and remains throughout this 

 stage as a darkly stained and homogeneous body apposed to the nuclear 

 membrane, where its affinity for the stain and smooth outline render it 

 extremely conspicuous. 



Primary Spermatocytes. 



After the last spermatogonial division, resulting in the formation of two 

 daughter primary spermatocytes, the nucleus is much reduced in size. 

 McClung has pointed out that at this stage reproduction is replaced by 

 constructive metabolism, and that the chromosomes, after exhausting their 

 metabolic resources, unite their common energies to build up a new 

 cytoplasm. This suggestion probably furnishes the true explanation, but in 

 any case possesses considerable pragmatic value, for some process of this 

 nature undoubtedly occurs. 



The cells undergoing this resting- or growth-stage occupy large areas in 

 the follicle, and the gradual increase in size as we proceed more and more 

 posteriorly is very noticeable. This growth-period is continued until the 

 nucleus has attained its maximum size, when the cell enters the prophase of 

 the next mitosis. Plate 1. figs. 6 & 7 show the difference between the 

 primary spermatocyte immediately after the secondary spermatogonial 

 division and immediately before the next mitosis. The nucleus shows a 

 reticulum, composed of chromatin granules placed along linin threads, the 

 individuality of the ordinary chromosomes being completely lost. 



It will be remembered that at this stage Sutton found no loss of 

 individuality of the chromosomes in Brachi/stola ; each chromosome under- 

 went resolution into a spireme in a separate sac, in which it remained 

 completely isolated, although the sacs fused at one end to form a common 

 chamber. He consequently met with no reticulum, or appearance of a 

 reticulum, and so put forward this phenomenon as a convincing proof of the 

 individuality of the chromosomes. Robertson observed a similar condition 

 in Syrhula, but did not always find the sacs, containing the ordinary 

 chromosomes, clearly distinguishable. Both Sutton and Robertson describe 

 a distinct vesicle, in which the heterotropic chromosome Hes, having no 

 morphological connection with the vesicles of the other chromosomes. I 

 have been unable to find the smallest trace of such vesicles, and am confirmed 

 in this by the work of Gerard on Stenohotlirus higuttulus—a member of the 

 same genus. 



