420 PROF. IS. T. LOWNE OH THE STRUCTURE AHD 
divergence of opinion; the identification of its nucleus with the 
germinal vesicle has been regarded as of the highest importance, 
and numerous attempts have been made to show that the nucleus 
of the egg-cell differs from those of the nutrient cells, from the 
very earliest stages of the egg-formation. Thus Dr. Claus (8) 
(p. 44) writes : — “ The questions, the answers to which are of the 
highest importance, are : from whence is the germinal vesicle 
derived? and what is its relation to the great yelk-cells ? The 
identification of the germinal vesicle appears to be difficult, and 
the earlier observers came to no certain result.” After quoting 
from Sir John Lubbock’s paper (19) he continues, “ I believe my 
own observations enable me to prove that the epithelial cells, the 
yelk-forming cells, and the egg-cell are modifications of originally 
identical elements.” Yet Claus thinks he distinguishes the 
germinal vesicle in very immature ova by “ its smaller size and 
clearer contents ” from the nuclei of the adjacent yelk-cells. 
Meyer’s (20) statements are in direct opposition to this ; according 
to these there are several germinal vesicles, each nucleus becomes 
invested by a membrane, each making, as it were, an attempt at 
forming an egg, the lowest nucleus persisting and the others 
disappearing. 
In my opinion by far the best and most accurate description of 
the development of the ovarian eggs in the Fly is due to Weis- 
mann (26) ; it is as follows : — “ The ovaries are developed very 
slowly in the Muscidse ; when the fly emerges from the pupa 
none of the eggs are formed, although the ovary may be recog- 
nized in the embryo” ( l . c. p. 206). Weismann then refers to 
a description of the ovary in the adult larva of the closely-allied 
Sarcopliaga carnaria (at page 134), “ Concerning the female sexual 
organs in the larva of Musca vomitoria I have no observations ; 
I must therefore fall back on those on the closely-allied S. car- 
naria. In a larva one centimetre long, the ovary has a diameter of 
0 , 29 m , is flask-shaped, and differs in its histological structure from 
the male sexual gland ; here we find no mother-cells, the struc- 
tureless sheath encloses only small round cells •013 m in diameter 
with nuclei ’01 m , exceedingly clear and exhibiting nucleoli. These 
cells are isolated with difficulty, as they adhere closely to each 
other. If we tear the ovarium of an adult larva no further 
structure is visible; but if a gentle pressure be applied to the 
uninjured ovary one may distinguish the first rudiments of the 
ovarian tubes. In the upper half of the ovary they appear as 
