BANCROFT: OVOGENESIS IN DISTAPLIA OCCIDENTALIS. 93 



cell, for, very shortly after the egg enters the water, into which it is 

 extruded, all of the follicle cells are lost, and the egg is covered only 

 by the chorion, with a few cellular fragments adhering to its outer 

 surface. It seems rather to be some product of the intense metabolism 

 of the cell, which the latter is attempting to get rid of, or to deposit in 

 some innocuous form. 



The degenerative changes in the test cells are much more complex, 

 ending in a product that looks like Figure 46 (Plate 5) when stained 

 with a nuclear stain, and like Figures 42 and 43 (Plate 5) when 

 overstained in safranin. The latter stain brings out the essential 

 structure more clearly, and by means of it we see that the test cell has 

 resolved itself into a number of vesicles (vs.), each one of wliich con- 

 tains a central refractive, faintly staining corpuscle (cp. c). The num- 

 ber of vesicles varies from seven or eight to twice that number. They 

 are remarkably uniform in size, and when well stained it is only very 

 rarely that one is encountered which lacks the corpuscle, though it 

 often happens that nuclear stains do not bring out the corpuscles at all 

 satisfactorily. At the centre of the cell there is accumulated another 

 substance, which sends out thin lamellae between the vesicles. In 

 haematoxylin preparations (Plate 5, Figs. 44-46), the central sub- 

 stance appears homogeneous or finely granular, but safranin demon- 

 strates within it quite a number of very deeply staining bodies that 

 sometimes occupy almost the whole central space (Fig. 43). Of the 

 nucleus, not a trace can be seen, for, as will be shown presently, the 

 central bodies just mentioned are not composed of nuclear material. 



The first step in the formation of these complex test cells begins early, 

 not very long after the formation of the test cells themselves, and 

 before the yolk granules appear. The first change noticed is an 

 irregular vacuolation of the cytoplasm (Plate 5, Figs. 35, 36). With- 

 in many of these vacuoles are seen bodies {cp. ia'vac.) which look 

 much like the central corpuscles of the vesicles of the final product, so 

 that it is most natural to suppose that the vesicles are developed from 

 the vacuoles of the earlier stage. But the conditions subsequently 

 encountered do not bear out this supposition. 



The next step consists in further vacuolation, which is still more 

 irregular. Some of these vacuoles are much larger than any of the 

 vesicles of the final stage (Plate 5, Fig. 37) , and occasionally three- 

 quarters of the cell will be taken up by an immense vacuole crowding 

 the smaller ones and their central bodies to one end. Furthermore, 

 nearly half of the vacuoles have no stained bodies within them, 



