2 
the whole, the sheets presented, even under considerable magnifying power, 
an exact mould of the structure of the wood, showing both the longitudinal 
ducts and the transverse markings, so familiar to all who were acquainted 
with the microscopic appearance of thin sections of wood. 
Dr. Henry Fripp then read a paper upon " Recent Discoveries in 
Insect Einbryogeny," of which the following is an abstract kindly furnished 
by the author. 
Dr. Fripp gave an account of the recent discoveries of Wagner, 
Meinert, Pagenstecher, Ganine, and Leuckart, respecting the propagation 
of larval broods of Miastor metralous and Oligaries (two new species of 
Cecidomyiae), and remarked that fresh instances would probably come to 
light as observations were extended. On comparing the several accounts 
of the authors above-named, great diversity of opinion appeared to exist 
respecting the source of the " germs " or " pseudova," from which the 
successive broods were produced. All, however, agreed in tracing back a 
thread of genetic connection between the larval broods and progenitors 
possessing the characters of maturely-developed and perfect insects. The 
phenomena were referred therefore to the well-known case of " alternate 
generations." The points of interest to be discussed involved questions 
of structure and of function. Firstly, the actual histological facts of the 
case ; secondly, the anatomical interpretation of these facts ; and lastly, 
the physiological inferences that might be drawn from them. 
1. The true derivation of the larve-germ. Taking as a starting-point 
the veritable egg of the female insect, we find that it is remarkably large, 
pud furnished with a micropyle, which sufficiently proves its capacity for 
fertilisation. It contains a germinal vesicle and vitelline matter, which 
undergoes the process of segmentation, and an embryo is developed ac- 
cording to the ordinary type of formation. This embryo reaches the con- 
dition of a perfect larva, (The very complex and perfect organisation of 
this larva was described and illustrated by diagrams). From the concurrent 
testimony of all the above-named writers it may be received as proved, that 
a portion of the contents of the egg not employed in the formation of the 
larva was enclosed within its body, and though by Messrs. Wagner and 
Meinert it was maintained that this residual matter actually became con- 
verted into " adipose tissue," the other naturalists agree in considering 
that it constituted a special organ, in fact, a sexual gland analogous in 
function with the ovary of a mature insect. This internal organ, therefore, 
immediately derived from cell elements existing in the original egg, possesses 
the power and function of a reproductive apparatus. So far, then, a 
direct continuity of genetic act, and a direct succession of organic elements 
specialised for a given function, may be assumed. In the next place it is 
proved that from this reproductive body germ- cells are produced, which 
histologically correspond with the 'pseudova' of other iusects and various in, 
yertcbrate animals. Within the body of the larva formed from the egg, 
