238 THE EMBRYOLOGY OF THE HONEY BEE 



complex within the yolk. This complex of course includes the 

 yolk cells, the latter, as already stated, being linked together by fine 

 processes to form a complex virtually constituting a syncitium. 

 Moreover, although the nuclei of the yolk cells degenerate, the 

 cytoplasm of these cells is never observed in a state of degenera- 

 tion. It seems not improbable therefore that this may be trans- 

 ferred by streaming movements to other cells less abundantly 

 supplied. 



During Stages IV to VII the general aspect of the yolk changes 

 but little. The cells of the cephalo-dorsal body enter the yolk at 

 the anterior end of the egg at Stage VII, as described in a pre- 

 vious section. In preparations of Stage IV multinuclear yolk 

 cells are still to be seen (Fig. 19) but they are wanting in those of 

 later stages. Aside from the cells of the cephalo-dorsal body, 

 the cells present in the yolk, up to Stage VII, are quite uniformly 

 distributed and of moderate size, each containing a nucelus whose 

 diameter seldom exceeds twice that of the nuclei of the blasto- 

 derm or its derivatives. The cytoplasm accompanying these 

 nuclei is relatively small in quantity and lacks the dark- staining 

 qualities and consequent opacity seen at earlier stages (see Figs. 

 19 and 20). 



At the close of the period of the formation of the blastoderm, 

 when the rudiments of the mesenteron and the mesoderm are 

 beginning to show themselves (Stage IV), the cells of the blasto- 

 derm become sharply demarcated from the yolk. Up to this time 

 the bases of the cells of the blastoderm have been intimately con- 

 nected with the protoplasmic network of the yolV, and form a 

 zone of dark-stained and much vacuolated cytoplasm, the inner 

 cortical layer (see p. 31). This central portion of the blas- 

 toderm cells now definitely separates from the blastoderm, remain- 

 ing in connection with the yolk. The inner surface of the 

 blastoderm and the outer surface of the yolk then acquire a sharp 

 and definite outline. The inner cortical layer now forms a thin pro- 

 toplasmic pellicle around the entire yolk mass enclosing it like a sac 

 (Figs. 18, 19, 24, 26). The peripherally situated yolk nuclei 

 naturally enter into a close relation to the surface layer, and this 

 relation is maintained to near the close of embryonic development. 

 These 'nuclei are, however, at first few and scattered, but after the 



