144 Harry Lewis Wieman. 



the germ cells. However, as will be shown later, the accumulation 

 of these cells at the lower end of the terminal chamber seems to 

 be involved in the differentiation of the germ cells, and it may be 

 therefore, that these form changes are simply due to mechanical 

 pressure as the cells make their way down the tube. Fig. 4 is a 

 cross section of an ovariole showing the same relationship. 



During the next few days the terminal thread undergoes a 

 remarkable growth, as a result of which its diameter is increased 

 enormously. In Fig. 5 is seen a longitudinal section of it at max- 

 mum development, when it greatly exceeds the terminal chamber 

 in volume. The same figure shows another stage in the formation 

 of the peritoneal sheath, which for the sake of simplicity was omit- 

 ted from several of the preceding drawings. Fig. 10 is from a pupa 

 about two days older, in which itisan be readily noted that the 

 terminal thread has diminished very considerably in volume. The 

 process continues until in the adult it has the appearance shown in 

 Fig. 13, where throughout the greater part of its length there is 

 evidence of degeneration, leaving at its base a cap-like mass of 

 cells which is practically all that remains of the structure shown 

 in Fig. 5. 



Fig. 10 shows at the base of the terminal chamber the first ap- 

 pearance of the limiting membrane, which comes into existence 

 first at the periphery, so that the center is the last part to be closed 

 off. The principle evidence for this is the fact, that for a consider- 

 able time after it can be definitely made out at the sides, groups 

 of epithelial cells can be seen in the central region entering the 

 terminal chamber. The membrane does not show any cellular 

 structure, and is probably a product of secretion of the epithelial 

 cells at the base of the terminal thread. 



Wagner ('36, '37), Siebold ('71), Will ('85), and others early op- 

 posed the idea of the terminal thread functioning in a purely 

 mechanical manner as a suspensary ligament for the ovariole, 

 and maintained that it is the place where the "Keimstatte" are 

 produced, w^hich in the lower part of the egg tube surround the 

 germ cells. Brandt ('78) thought this interpretation might apply 

 in forms where there was direct continuity between the terminal 

 chamber and thread, but where the two regions are separated by 



