DEVELOPMENT OE THE OYAETES IN THE BLOWELT. 



421 



cylindrical follicles lying parallel to each other. They are all 

 united above without any point (terminal thread ?) being visible, 

 below tliey are lost in the cellular mass. The diameter of a 

 follicle averages '04 ™. 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) " 8o that, as I have 

 shown above, the original solt 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 flnsk-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 draAvn 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 



