290 



EMBRYOLOGY OF INSECTS AND MYRIAPODS 



becomes the embryonic rudiment; the other layer, the envelope. This 

 pecuHar condition, where the yolk, instead of lying inside the vesicle 

 formed by the primary epithelium (blastoderm) comes to lie outside of it, 

 was first described by Brues (1903) for Xenos peckii. 













Fig. 223. — Stylops praecocis. 

 ginning of germ band (gb). 

 Amnion, (y) Yolk. 



(am) 



Fig. 224. — Stylops praecocis. Longi- 

 tudinal section, (gb) Germ band, (y) 

 Yolk. 



Noskiewicz and Poluszynski homologize the envelope of Stylops with 

 the envelope of Isotoma, concluding that it represents both amnion and 

 serosa. Since it has the appearance, however, of the amnion alone, for 

 convenience it is here designated as the "amnion." Multiphcation of 

 cells in the embryonic rudiment is indicated by the mitotic figures. 





Fig. 225. — Stylops gwynatme. Lon- 

 gitudinal section, (am) Amnion, (gb) 

 Germ band, (y) Yolk. 



Fig. 226. — Stylops praecocis. Longitu- 

 dinal section, (am) Amnion, {antr) An- 

 terior end. (par) Paracyte cell, (post) 

 Posterior end. (y) Yolk. 



If, as some embryologists insist, the yolk cells are to be regarded as 

 the primary entoderm, the sphere of cells first formed should not properly 

 be called a "blastoderm," since some of its cells form the envelope, taking 

 no part in the formation of the embryonic rudiment. For convenience, 

 however, the term "blastoderm" will be used. The digestive epithelial 



