DEVELOPMENT OF PARAVORTEX GEMELLIPARA 527 



preceding section on the sex organ and vitellarium anlagen, 

 ultimately differentiate to form the viteUine cells. Their devel- 

 opment will be considered later. 



In P. gemellipara the intestine is organised from cells which, 

 at the stage illustrated by figures 35 and 36, are proliferated in 

 the region just posterior to the oesophagus. Two of these in 

 figure 26 were pointed out above while the pharynx was being 

 considered. It is believed that they are derivatives of the large 

 clear cells designated as ent. 2 in figure 23. 



With the rapid absorption of the yolk inside the secondary 

 entoderm cells, the latter become enclosed with the epithelial 

 cells which, arising in the manner above described, migrate 

 backward about and between them. In this way a loose rod of 

 cells comes to occupy the whole region behind the pharynx. 

 As Hallez observed, the intestinal lumen first appears at the 

 anterior end of the rod, and gradually extends posteriorly. As 

 long as the young worm remains in the capsule there is no com- 

 munication with the outside through the pharynx and mouth. 

 It is probable, however, that it is potentially present, requiring 

 only the muscular activity of the pharynx to open the lumen. 

 The young animals, when liberated from the mother by pressure 

 upon the cover-slip, exhibit contraction and expansion of the 

 pharyngeal apparatus, a feature which indicates that, as soon 

 as they are in a position to obtain food from without, they are 

 provided with a lumen from mouth to intestine. 



i. Glands. Shortly before the young worm leaves the capsule 

 from two to four elongated oval or spindle-shaped bodies appear 

 between the brain and the vertex of the anterior end of the body 

 (fig. 45). In iron-haematoxylin preparations these masses are 

 grayish in color, while Ehrlich's stain imparts to them a deep 

 red. In animals which have entered the tissues of the mother 

 these gray bodies communicate with the exterior (fig. 46) by 

 slender processes; they are now recognizable as the cephalic 

 glands. To these has been attributed the function of secreting 

 a slime which lubricates the animal's path. 



Numerous other spindle-shaped cells distributed through the 

 sub-epithelial tissue are evidently single-celled glands which 

 have to do with the secretion of mucous. 



