230 



AYERS ON THE DEVELOPMENT 



,tOt 



Fig. 7. 



Fig. 8. 



may be flattened against one another but at all times a cell wall is to be distinguished. 



These cells have large nuclei with prominent nucleoli while the cell substance is found as 



an exceedingly thin layer covering the nucleus. The nuclear boundary is even more 



distinct than the cell boundary. Nuclei in the upper and middle part of the germarium 



seldom have more than one nucleolus and may be destitute of such a structure, while in 



the lower part and in the enlarged mouth two or three nucleoli are frequently found in 



each nucleus. These nuclei are amoeboid, their changes in form being most noticeable 



in the lower part of the germarium. In pi. 20, figs. 25, 26, 27, and pi. 21, fig. 25 are 



shown the structure and relations of the germ cells to the tunica propria. These germs 



pass down the tube into the upper end of the vitellarium where they become surrounded 



by a greatly increased amount of finely granular protoplasm that is in intimate contact 



with the epithelial lining of the vitellarium. (PI. 20, figs. 1, 2, 3, 5, 27; pi. 21, figs. 28, 29, 30 and 



Figs. 2-6, on p. 229.) This epithelial lining, or follicular epithelium, is confined strictly to the 



vitellarium, in the upper part of which it is seen as a membrane one 



cell deep, either lining the walls of the tube or extending between 



and about the ova, thus separating them from each other and from the 



tunica. These epithelial cells are somewhat smaller than the germ 



cells found in the lower part of the germarium, and the relative 



amount of nuclear and cell substance is different in the two cases. 



The germ cells have a greater proportion of nuclear substance. The 



epithelial cells proliferate rapidly and soon increase the extent and 



thickness of the follicular membrane, which is at all times thinnest 



at its upper end, where it grows around the ovum in a thin sheet 



of small cells. In no case was a cell which from its size indicated 



its origin in the germarium found in process of division after reaching 



whereas, in the germarium itself cells in such a condition are sometimes 



egg advances toward the oviducal end of the ovariole the wall of 



the epithelial follicle becomes thicker and more capacious from the 



increase in the number of cells composing it. 



The germinative vesicle, which is the transformed nucleus of the 

 germ cell, becomes vesicular and at the same time acquires several 

 nucleoli, which gradually enlarge but remain connected with each 

 other and with the nuclear membrane by numerous tortuous fila- 

 ments. Sometimes there is a single nucleolus and then the nuclear 

 filaments are much more numerous. The nuclear fibres or threads 

 are to be seen only aftert reatment with certain reagents (e. g. 

 gold chloride, silver nitrate, osmic, chromic and acetic acids). The 

 germinative vesicle is distinctly amoeboid in the upper follicles but 

 shows this characteristic to a less degree in the two or three folli- 

 cles before the one in which it disappears, while in the latter its 

 amoeboid nature is again asserted. Its membrane is distinct until 

 about the time of its disappearance, which occurs in the following 

 manner. Near the time when the vitelline membrane is secreted, 

 the wall of the germinative vesicle grows thinner. 1 It remains sharply marked off from 



1 For a comparison of the different stages of this process in other animals see Bambeke (2), Van Beneclen (3 and 4), Brandt (9). 



Fig. 7. Diagram of the forma- 

 tion of an egg follicle. 



Fig. 8. An ovariole of Oecan- 

 thus from a dissection in distilled 

 water, x 70. 



the vitellarium, 

 found. As the 



Fig. 8, a. 

 Fig. 8, a. Set tion passing trans- 

 versely through an epithelial par- 

 tition between two follicles. From 

 an osmic acid preparation of an 

 ovariole of Oecanthus. X 600. 



