DEVELOPMENT OF PARACOPIDOSOMOPSIS 19 



39), and gradually becomes scattered throughout the cytoplasm 

 of the two daughter cells (fig. 40). In the fourteen-celled stage 

 these two blastomeres are recognized easily, owing to the presence 

 of the nucleolar granules, which cause the cytoplasm to take a 

 deeper stain (figs. 41, 42). They lie well toward the top of the 

 group of enclosed embryonic cells. 



It is clear that the presence of the nucleolus or its material 

 exerts a retarding influence on the divisions of the cells which 

 happen to inherit it. The inhibitory influence is sometimes 

 shown in the formation of the eight-celled stage from the four. 

 In some eggs (text fig, 1, 0, P) while the nucleus of the nucleolar 

 blastomere is still in the prophase condition, the spindles of the 

 other three cells have reached the metaphase stage. 



The fact that the nucleolar substance retards divisions has 

 been noted by other investigators. Silvestri ('06, '08) observed 

 this phenomena in the eggs of Litomastix and Ageniaspis, and 

 Martin ('14) has shown in the egg of the latter species that in 

 the two-celled stage the nucleolar blastomere does not divide 

 so quickly as the sister cell. There is thus produced a typical 

 three-celled stage. At this point of development the nucleolus 

 breaks down and cannot be traced further. 



e. The fifth divisioyi 



In the fifth division all of the blastomeres, including the two 

 which inherited the nucleolus material, divide, thus producing 

 twenty-eight cells. In this stage one can still recognize the four 

 descendants of the original nucleolar cell by the fact that the 

 granules in their cytoplasm cause them to take a deeper stain than 

 the other embryonic cells. In figure 43 three of these cells are 

 clearly seen; the other lies in an adjacent section. The egg 

 from which the figure is drawn has twenty-seven cells, but one 

 of the blastomeres is dividing to produce the typical twenty- 

 eight-celled stage. The cells do not form a solid mass, for owing 

 to their rounded condition many interstices are found. 



The polar region has formed a definite and complete membrane 

 around the blastomeres through the gradual movement of its 



