1884.) Entomology. $30 
segment, and “come to lie just behind but dorsad of the base of 
the third thoracic appendage.” The internal cavities of each gill 
“are continuous with the body-cavity, and probably serve as 
channels through which the vascular fluid circulates.” In sections 
of the gill-organ before becoming atrophied or absorbed, both 
distinct canals and lacunar spaces radiate from the point of con- 
nection of the pad with the body; “and these, together with the 
arrangement of the cells, give the radiate structure characteristic 
of the fresh gill.” “The gill pad is essentially a single-layered 
sac, with a much constricted neck, evaginated from the pleural 
region of the abdomen.” It should be observed that these are 
not tracheate gills, as they contain no trachee. Mr. Ayres does 
not speculate as to their origin. 
While not accepting Balfour’s interpretations and general con- 
clusions as to the origin and significance of the primitive germinal 
yers among the insecta, Mr. Ayers confesses himself still in doubt 
as to their origin. But, he adds, “ when we consider the rôle and 
subsequent fate of these two layers, it at once becomes apparent 
that such a view does not accord with the facts, for the blastoderm 
ultimately forms the entoderm (mesenteron), and the ectoderm, 
arising from a small area of thickened cells on one side of the blas- 
toderm, encloses the yolk and endoderm by a genuine epiboly.” 
With some hesitancy he then proposes an explanation which may 
‘pply to the Orthoptera: “How did the embryonic membranes 
(amnion and serosa) arise? What is their function? Is their pres- 
ent function the primitive one? The answer to these inquiries un- 
doubtedly lies in the clear comprehension of the relations of the 
embryo to its food supply—the yolk. That the cellular embryonic 
membranes could have originated for protection, or from an early 
Sedysis, is, to say the least, highly improbable. Among the in- 
co egg is furnished with a protective membrane—usually in 
Gon of a chorion—before leaving the body of the parent. 
i erae the interesting and original explanation in full, the result 
aid + in Ecanthus the membranes fuse at or near the head, 
Yy a self-eversion through the opening caused by their rup- 
STS ath comes to lie outside of the amnion and serosa. 
Penanda its thick walls finally disappear by a process of 
