140 



SYCANDRA. 



present. At the close of the next stage, forty-eight cells are pre- 

 sent arranged in four tiers (fig. 63 D and E), the two outer tiers 

 containing eight cells each, and the two inner sixteen. The two 

 inner tiers probably arise by the simultaneous appearance of two 

 equatorial furrows dividing the original tiers into two, and by the 

 subsequent simple division of the cells of the two inner of the 

 tiers so formed. At the close of the stage the eight basal cells 

 become granular (fig. 63 F). At the same time the central part 

 of the segmentation cavity becomes enlarged, while its terminal 

 apertures become narrowed and finally, shortly after the end of 

 this stage, closed. The axial perforation thus acquires the 



FIG. 64. LARVA OF SYCANDRA RAPHANUS AT PSEUDOGASTRULA STAGE, IN SITU 



IN THE MATERNAL TISSUES. (Copied from F. E. Schulze.) 



me. mesoblast of adult ; hy. collared cells forming hypoblast of the adult ; en. 

 clear cells of larva which eventually become involuted to form the hypoblast ; ec. 

 granular cells of larva which give rise to the epiblast, which at this stage are partially 

 involuted. 



character of a closed segmentation cavity. While the ovum 

 itself becomes at the same time a blastosphere. 



This stage nearly completes the segmentation : in the next 

 one, the cells of the poles of the blastosphere increase in number, 



