DESCRIPTION" OF PLATE H. 



Fig. 10. — Posterior appendage or micropyle of Apbis, 

 treated with weak potash solution : e, eminence rising 

 from the chorion h ; f, appendage containing rod-like 

 bodies ; r, gelatinous investment. After Huxley 



Fig. 11. — Ovum of Phyllaphis fagi soon after it has 

 been laid. It is sufficiently transparent to show (r) 

 the coarse segmentation ; m, polar opening or micro- 

 pyle. 40 diam. 



Fig. 12. — Part of the ovum of GaUipterus quercus 

 treated with acetic acid : s, annular congregation of 

 cells forming a polar mass or pronucleus (?), vide 

 Balfour, 1. c, p. 59. 



Fig. 13. — Centrolecithal* segmentation of the ovum 

 of Siphonophora rosce. Ovum is still in the ovisac. 

 n 7i, two clear nuclei have appeared, and they are 

 surrounded by v 9 the vitelline mass enclosed in a proto- 

 plasmic layer, I. 



Fig. 14. — The same more advanced ; in which the 

 protoplasmic layer has been differentiated into a series 

 (c c) of columnar cells ; p t the pole of the blastoderm, 

 which has no share in forming the embryo. 



These two figures are copied from Metschnikow. 



Fig. 15. — The germ-cup or gastrula-stage of Haeckel, 

 in which the blastoderm has become dented in, and 

 the original single membrane has become two. The 

 ends have approximated to form the intestinal cavity 

 or archenteron; and h, the stomodamm, blastopore, or 

 primitive mouth ; e, the entoderm or hypoblast ; /*, 

 the ectoderm or epiblast. 



Fig. 10. — A much magnified view of the ovum of 

 Aphis persicai still enclosed in the ovisac. It has 

 begun its incipient segmentation. At the pole (w) a 

 depression or invagination encloses a clear yellow 

 space, which is comparatively free from yolk granules. 

 The vitelline membrane is seen enfolding, r, the coarsely 

 granulated yolk, which last is passing into the mul- 

 berry-like segmentation. The granules congregate 



* From Klvrpov, a centre, and X^icvOoc, lecythus, an oil vessel. This 

 kind of segmentation is almost confined to the Arthropod a. 



