Bennet Mills Allen 125 



The rete tubules extend in a posterior direction, their bases remaining 

 attached to the peritoneum for a long time after the sex cords have 

 become completely separated from it. These rete tubules penetrate quite 

 deep into the stroma, reaching the walls of the Malpighian corpuscles, 

 to which they are often so closely approximated as to give the appear- 

 ance of arising from them. The glomeruli underlying this rete region 

 comprise those from the 6th to the 20th, inclusive, in the pig, and from 

 the 6th to the 12th in the rabbit. 



Since the rete remains indifferent in character long after the ovary 

 and testis have become differentiated from one another, a common de- 

 scription will suffice to make clear its development in both male and 

 female, up to a relatively late stage. Primitive sex cells begin to form 

 anew from the syncytial cells of the rete tubules in the pig embryo 

 of 3 cm. length. When the embryo has reached 4 cm. length, the rete 

 tubules break away from the peritoneum along the posterior three- 

 quarters of the length of the rete region. I was unable to determine 

 whether this process is similar to that by which the sex cords become 

 separated from the peritoneum. In any case it takes place at a much 

 later period as above shown. 



At this stage and a little earlier, evaginations arise from the capsules 

 of Bowman of the Malpighian corpuscles at points close to the mass 

 of rete tubules (Plate V, Fig. 15). Their number varies from 

 one to three. In fact many Malpighian corpuscles give off no evagina- 

 tions at all, although they arise in close proximity to the rete tubules. 

 Similar evaginations occur in the rabbit embryo of 16 and 17 days, 

 where they were first observed by Coert, 98. I am inclined to ascribe 

 to these a morphological significance, yet they are of no particular func- 

 tional importance, because a union of the rete tubules with the capsules 

 of Bowman is, in very many cases, established by the former coming in 

 direct contact with the latter. 



It is interesting to note that l^ranches from the rete tubules grow out 

 to meet the tips of the evaginations from the Malpighian corpuscles. 

 The cells from these two sources assume similar characters and are 

 later indistinguishable from one another. Such later stages are very 

 deceptive, having no doubt given rise to the incorrect view that the rete 

 tulmles arise from the Malpighian corpuscles. 



The rete tubules 1)ianch and anastomose in their course, behaving 

 much like the sex cords in this regard. The tubules of the anterior end 

 of the rete mass remain in connection with the peritoneum throughout 

 later stages while posterior to this point they are separated from it by 

 a considerable interval and are united to form a cylindrical mass, the 

 posterior end of which projects into the anterior end of the sex gland. 



