RECENT DISCOVERIES IN INSECT EMBRYOGENY. 
1*23 
stecher, a totally different aspect from these germs or ova. And 
the latter observer conjectures, that their origin might be traced 
back to one or all of three distinct histologic sources noticed by 
him : — 1st, to cells embedded in a tine granular mass, situated 
around the intestine in the last larval segment ; 2nd, to cells 
appearing very prominent immediately under the integument 
which unites the two last segments of the body ; and, 3rd, to 
the subcuticular layer of cells before mentioned. Pagenstecher 
was unable (from the dying off of his larvae) to carry on his 
researches, so as to discover a special reproductive organ. 
His account of the further development of these ova is as 
follows. By a process of segmentation, a vitelline mass is formed 
under its enveloping vitelline membrane, during which process 
the outer sphere of clear globules disappears. Then an embryo- 
nal cell-layer (including a number of oil-drops) separates itself 
from the vitelline mass. These two separate parts increase ra- 
pidly, and with equal volume at first, but as the development 
proceeds, the embryonal layer gradually overlaps the yolk-mass 
towards that end which becomes the head of the embryo. In 
larvae prematurely taken out of their envelopes, the residual 
yolk-mass is found pushed back to the posterior dorsal region, 
and is easily recognised. It might, therefore, be supposed to 
become transformed into fatty tissue, and the subsequent larval 
propagation thus brought into a certain genetic connection with 
the primal evolution of this fatty, or rather formative, material, 
derived from the original substance of the true egg. The idea of 
a true genetic descent is, by this explanation, still kept in view. 
As development proceeds, the parent larva is gradually filled and 
swelled out in form by the increase of size of the progeny within. 
Pagenstecher observed that the young broods undergo at least 
one moult during their growth. Each embryo now shows con- 
tractile and extensile movements of its .own, and having broken 
through its egg-coverings, moves freely about in the cavity of 
the parent body. The parent larva then secretes from the 
inner surface of its skin (or subcuticular lining-cell mem- 
brane), a kind of second inner skin, which is, however, incom- 
plete at the extremities. With these two skins it still lives for 
a time, making movements as of extrication, which sometimes 
cause the outer skin to give way. On ceasing to live, the 
parent becomes a sort of pupa covering, or substitute for it, 
to the brood within, which voraciously devours the maternal 
viscera. Pagenstecher found in his beetroot refuse many empty 
perforated sacs, the remains of the parents from which the 
young had escaped. 
This observer thus sums up his record : — From some part of 
the body, not yet determined, ovales are detached, which fall 
free in the larval body, and are transformed into ova by a 
