88 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



bedeutende Kolle spielen, allein einstweilen dtirfte man die Frage nach 

 ihrer eigentlichea Fimction und ihrer richtigen Deutung gewissermassen 

 als eine offene bezeichnen konnen." 



In considering the function of the test cells, it should always he borne 

 in mind that they are follicle cells derived from other follicle cells and 

 as such their mission is to convey nourishment to the ovum. The fact 

 that they lie under the chorion, and imbedded in the cytoplasm of the 

 ovum, does not remove them from this category, but merely puts them 

 in a more favorable position for conveying food to the egg cell. Start- 

 ing as normal and vigorous cells in the follicular epithelium, their ac- 

 tivity is so great that degenerative changes in the shape of vacuolation 

 appear in them, while the follicle cells proper still retain their normal 

 appearance. The early occurrence and complexity of these processes offer 

 the best possible evidence for the intensity of the activity. It is not sur- 

 prising, therefore, aud I think we have no right, a priori, to expect that 



cells which have worked so hard that they have lost their vitality 



cells in which degenerative changes have set in — should become further 

 involved in the developmental processes of the embryo. 



3. Secondary Follicular Epithelium. 



For some time after its complete differentiation this epithelium is 

 comparatively thin with flattened nuclei (Plate 4, Fig. 27). Soon, 

 however, as the cells multiply, the epithelium thickens, and the nuclei 

 assume a spherical shape (Plate 3, Figs. 26, 15, e'th. fol). The in- 

 crease in cells continues, so that soon they must arrange themselves 

 in two layers (Plate 4, Fig. 28). At about this stage morphological 

 differentiation sets in, and the inner nuclei fail to take the stain strongly, 

 thus becoming somewhat paler than before (Fig. 28, nl. e'th. fol. i.). 

 All cell multiplication now seems to cease, for with the subsequent 

 growth of the ovum the thickness of the follicle decreases, probably on 

 account of stretching (Plate 5, Fig. 30). But in spite of this thinnin^ 

 out the follicle does not become one cell thick, as Davidoff maintains' 

 (p. 136). On the contrary, there are two quite distinct kinds of nuclei 

 (Fig. 30), and it is probable that at this stage the inner and outer follic- 

 ular epithelia are differentiated, but so closely pressed together that the 

 only indication of the differentiation consists in the nuclei. 



4. Inner Follicular Epithelium. 



It must be confessed that while the egg is still in the ovary the nuclei 

 of this layer are hard to find, and do not appear to be numerous. More- 



