1885. ] Entomology. NRE 
rior poles of the egg are determined by its position in the ovarian 
tubule, in which it remains during its whole course of develop- 
ment. 
2. Segmentation and formation of Blastoderm—The segmenta- 
tion instead of being superficial, as usually described, is endo- 
vitelline. The germinal sac dissolves, and its nucleus divides 
repeatedly, forming a large number of nuclei within the yolk. 
The nuclei have amceboid movements, and go towards the poste- 
rior pole (PE)? and thence spread over the surface-protoplasm. 
A few of the nuclei remain in the center; but the great majority 
become distributed over the surface, where each forms a center of 
attraction for the protoplasm. Thus a layer of cells is formed 
over the whole surface, the cells being smaller and more numer- 
ous towards the posterior pole, which is most active in its rate of 
development (Fig. 1). This layer is the blastoderm. A few cells 
are subsequently forme 
lation, showing a transi- 
tion to epiboly, in which 
the peripheric protoplasm 
would be confined to the Fig. 1. Fig. 2. 
spot over the germinal Fic. 1.—Ovum with blastoderm completed and 
sac. The largeness of the pseudovitellus beginning to invaginate. Fic. 2. 
g and the distribution _,Cermstrenk, lateral plates and amnion sre 
of protoplasm all over the era enclosing genital layer and part of germ- 
surface, cause the differ- str 
ence. The few cells mesoblast. 
formed in the center represent the endoderm. 
3. Peculiar to Aphides—Cells from the epithelium of the ova- 
rian tube form an appendage to the posterior pole of the egg. A 
single cell is given off from these, which repeatedly divides so as 
to become a cell-mass. These increase by absorbing food, and 
afterwards became invaginated as a greenish mass, called pseudo- 
vitellus (ps). This is destined to be received dorsally into the 
embryo and to become paired masses in the abdomen. The 
- Explanation of reference letters in the figures; 4B, abdomen; AP, anterior 
pole; HD, head; PP, posterior pole; TA, thurax; am, amnion ; at, antenne ; d/, 
blastoderm ; br, brain ; a, lioda; ge, generative cells; ; g5, germ- streak ; ; dp lateral 
plate; md, ma ndible; ma! mx?, first and second m aille; a ot, ovarian tube cells; 
r ?’; first, second and third thoracic limba i pe, EEA part; pre, proctodæ- 
um ; fs, ss cldeeettiDhins se, serous layer; sg, salivary corr st, stomodzeum ; y, yolk. 
