DEVELOPMENT OF THE OVARIES IN THE BLOWFLY. 421 
cylindrical follicles lying parallel to each other. They are all 
united above without any point (terminal thread ?) being visible, 
below they are lost in the cellular mass. The diameter of a 
follicle averages ‘04 m . The ovarian follicles consist of a sheath 
of fine structureless membrane and its contents, which differs in 
no way from the surrounding cell-mass. The sheaths are a cuti- 
cular excretion from the outer surface of the cells forming the 
cylinders.” (He continues on page 206) “ So that, as I have 
shown above, the original soft mass of cells with which the 
ovarian capsule is filled becomes differentiated, in part, into solid 
strings, which shed a cuticle from their surface, and the ovary 
comes to consist of a small-celled ground-substance which fills 
the capsule, in which solid cellular strings are imbedded, each 
enclosed in a fine structureless membrane; of an outer and inner 
epithelium, a tender albuminous contents in which free nuclei are 
imbedded, as Meyer describes in the youngest condition of the 
ovary, there is as yet no trace. The term egg-tubes is hardly 
admissible at this stage, it is only later by the differentiation into 
a wall and contents that they become tubes.” 
“ On the seventh day of the pupa stage the egg-tubes still only 
occupy a small zone of the flask-shaped ovarium (Taf. xiv. fig. 70); 
they lie close together parallel to the long axis of the ovary and 
still exhibit their original simple structure, only the contained 
cells are somewhat larger and therefore more distinctly seen. 
These cells are spherical, and their nuclei are easily distinguished. 
The cuticular sheaths end above in rounded domes.” 
“ By the fourteenth day the investing sheaths of the egg-tubes 
are considerably more developed, and their outer form is altered; 
the blind end is now drawn out into a point, the middle part is 
swollen and the posterior part contracted. Still the lumen is 
filled with cells disposed without definite order ; no regular epi- 
thelium is yet visible, but there is a great difference in the size 
of the cells, the central ones being larger than those of the 
periphery. A little later these changes are more conspicuous, 
and the egg-tube exhibits a stem, a chamber, and a nipple-like 
appendage ” [Stein’s end-chamber], “ the narrowed blind end of 
the tube. In the chamber there is a distinct separation of the cells, 
small cells line the follicle in a single layer, as an epithelium 
enclosing the larger cells ; from the latter the egg is ultimately 
formed.” 
“ The development of the ovary shows that the life of the fly 
