SEXUAL ORGANS AND THE I H PRODUCTS IN PHORONIS. 



149 



possession of only three chromosomes of maternal origin. Exactly the 

 same reduction occurs during the formation of spermatids, as will soon 

 be pointed out. 



The Testis and Its Products. — As to the development of the testis 

 I have not been able to obtain as clear an insight as in the case of the 

 ovary. However it may safely be said that the inceptional condition as 

 well as the general manner of development are essentially the same. 

 The small and flat peritoneal cells, remaining beneath the nutriment layer, 

 proliferates, thus forming a crowded assemblage of small spermatogonia 

 around a capillary at its basal portion. This is the first Anlage of the 

 testicular tissue. As the spermatogonia increase in number, the over- 

 lying nutriment layer is lifted up by them ; at the same time its cells be- 

 come smaller and are evidently on the way of becoming totally resorbed, 

 in much the same way as we have seen in the case of the ovary. Mean- 

 while, what is peculiar to the testis, the connective-tissue layer sends 

 out fibrous bundles outwards and radially into the assemblage of sper- 

 matogonia, which soon arrange themselves around and along each of the 

 said connective-tissue bundles. The spermatogonia thus form radial 

 strings, the testicular strings, of which the connective-tissue bundle con- 

 stitutes the axis. With the disappearance of the covering nutriment 

 layer, the strings are somewhat loosened in their relation to one another 

 and are seen to beset the capillary surface in a villi-like manner. 



The above changes on a testicular capillary proceeds from the base 

 distally towards the blind end. We may say that the testicular Anlage, 

 consisting of a mass of spermatogonia traversed by radial fibrous 

 bundles and covered over by the degenerating nutriment layer, shifts 

 its position in the said directon, leaving behind it the testicular 

 tissue just developed in the form of uncovered cellular strings and 

 ever encroaching upon and lessening the domain of the nutriment 

 layer in front of it. The advance of the growing end of the testicular 

 tissue takes place in that the flat piritoneal cells remaining beneath the 

 nutriment layer undergo proliferation in sita and thus give rise to new 

 spermatogonia. The development of a testicular capillary is complete 



