DEVELOPMENT OF PARA VORTEX GEMELLIPARA 537 



calation between the yolk-laden primary entoderm cells of new 

 cells derived from the secondary entodermic elements which 

 durmg gastrulation remain in the region just posterior to the 

 oesophagus. 



11. The approximate time of appearance waS noted for the 

 subdermal glands and those of the alimentary tract; they are 

 not present in the young w^orm at the time it leaves the mother, 

 but have already developed in free-living specimens which have 

 reached a length of 0.30 mm. 



12. The cephalic glands appear in the embryo while it still 

 lies in the capsule. There are three single-celled glands which 

 develop in the mesenchyme between and anterior to the eyes. 

 By the time the young worm is ready to leave the mother these 

 glands have each become connected with the exterior through 

 a fine process which penetrates the anterior body covering. 



13. During very early embryonic life the vitellogenous cells 

 migrate backward from the region of the gonads — just posterior 

 to the pharynx. Most of them become grouped in the pos- 

 terior end of the body, but a number come to rest at various 

 points beneath the ectoderm in the posterior two thirds of the 

 body. The vitellaria develop first from the large mass of cells 

 between the intestine and the body wall and push gradually 

 forward till they effect a union with, the posterior end of the 

 antrum. Meanwhile the isolated cells divide to form groups 

 which soon anastomose with the main portions of the glands. 



The testis and ovary of each side of the body become differ- 

 entiated from a single gonad, the former arising from the an- 

 terior and the latter from the posterior end. In a 0.30 mm. 

 embryo the two glands have become separated. Meanwhile 

 a large group of cells has accumulated in the mid-ventral line 

 between intestine and body wall. The anterior portion of this 

 mass proliferates cells which surround the testis with a flat 

 external epithelium and also form the vasa deferentia. The 

 seminal vesicle arises in the next posterior portion of the mass 

 by a rearrangement of cells about a lumen. It is composed 

 of two layers of epithelia. At the same time the atrium com- 

 mune develops in a similar manner. At this stage the antrum 



