DESCRIPTION OF PLATE H. 



Development of the Ovum in Aphis. 



Fig. 1. — A young ovum before segmentation has 

 commenced, b. body of ovum ; g, germinal vesicle ; 

 s, germinal spot ; n, nucleolus. After Haeckel. 



Figs'. 2, 3, 4, 5. — Ova in different successive stages 

 of segmentation or division into 2, 4, 8, &c. cells until 

 the mulberry- form or morula-stage of Haeckel is at- 

 tained. The cell ultimately forms a double wall, enclos- 

 ing a central cavity with blastospore. 



Fig. 6. — An ovum in process of fecundation by the 

 intrusion of the spermatozoa, by the action of which 

 segmentation commences : z, zona pellucida ; g, ger- 

 minal vesicle ; n, spot and nucleolus ; sp, spermatozoa 

 just before penetration into the body of the egg. 



The foregoing six figures, after Haeckel, are dia- 

 grammatic, and are only generally applicable to 

 Aphides. 



Figs. 7 and 8. — Polar cells and micropyles (?) of 

 the ova of Lachmis longipes : 1 1, represents the spindle 

 of Fol (?) formed from the metamorphosis of the 

 germinal vesicle ; s s, stellate body forming part of 

 the eminence rising out of the chorion ; r r, gelatinous 

 investment of Huxley. This would appear to be the 

 polar appendage of Balbiani. Treatment with acetic 

 acid. 112 diam. 



Fig. 9. — Polar mass and appendage of the ovum of 

 Aphis persicce : a, probably represents the spindle of 

 Fol; p, the polar mass studded with green cells. The 

 appendage is surrounded by an epithelial layer. After 

 Balbiani. 



