DEVELOPMENT OF PARA VORTEX GEMELLIPARA 511 



ably a large part of this clear region is occupied by a f uid of a 

 watery nature which has been absorbed from the parenchyma. 

 It was pointed out above that capsules which are freed in sea 

 water immediately swell on account of pressure due to water 

 absorption. 



8. Organogenesis to the time of birth 



a. Origin and development of the eyes. The first organs to be 

 differentiated from the mes-ectodermic mass in Paravortex 

 gemellipara are the eyes. Although at first this seems rather 



etft:- 



Text fig. 16 Surface view of an embryo which of its own account had made 

 Its way into the mother's parenchyma, ent.l., digested remains of yolk in pri- 

 mary entoderm cells; e, eye. X 400. 



remarkable, still it is reasonable to expect that, since the major 

 portion of each definitive eye consists of a single cell, this cell 

 must at an early stage take on a different appearance from those 

 about it. Already in figure 24 the eye cell shown has become 

 distinct by its larger size and clearer cytoplasm. 



These eye cells appear, one on either side toward the dorsal 

 side of the undifferentiated mass. That seen in figure 24, an 

 oblique frontal section, is an individual cell with a distinct 

 membrane (Hallez was unable to distinguish the membrane in 

 P. cardii) and nucleus. The latter at first lies in the center of the 

 cell, but soon assumes an eccentric position toward the posterior 

 median side. The presence of only a single melanin granule is 

 certain on account of the fact that the whole cell is included in 



