MUSEUM OF COMPARATIVE ZOOLOGY. 139 



In the early stages of their development the tubules have a more or 

 less spiral course, while in the later stages they become more nearly 

 straight. In February eggs (Fig. 25, Plate III.) their inner ends are 

 slightly expanded, and terminate in a thin structureless film overlying 

 the zona. In radial sections of eggs taken in May, they often appear 

 triangular at the base, and their contents divide into branches which 

 enter the pores of the zona. The " filaments " connecting the canals 

 are sometimes much more abundant than at others. In the vicinity of 

 the micropyle one finds on tangential sections (Fig. 31, Plate II.) that 

 the tubules at or near their bases are joined to each other by what 

 appear like slender filaments, but these may be the cut edges of nearly 

 perpendicular membranes. This results in the production of an irregu- 

 lar network with meshes of variable size and shape, at the angles of 

 which the spiral tubules are located. 



The micropyle was seen in eggs taken in February and in May. 

 Immediately surrounding it, the zona radiata is thickened by a slight 

 elevation of its internal surface (Fig. 24, Plate III.). The micropyle con- 

 sists of a funnel-shaped opening in the zona with the wide end directed 

 outward. In some cases the inner end of the canal also flares slightly. 

 In a February egg in which the micropylar region was somewhat distorted 

 (Fig. 26, Plate II.) the micropyle seems to have been composed of two 

 regions, separated from each other by a distinct shoulder, the inner 

 end of the outer portion being much wider than the outer end of the 

 inner portion. The granulosa cells and their tubules are greatly crowded 

 above this region (Fig. 24, Plate III.). At some distance on either 

 side of the micropyle it is to be seen that the outer funnel-shaped ends 

 of the canals begin to be more elongated than in other parts of the egg, 

 and continue to increase in length up to the micropyle. The nuclei of 

 the granulosa cells, which are situated near the bottom of the funnel- 

 shaped expansions, also become more and more elongated as one ap- 

 proaches the centre of the micropylar region, and at the same time they 

 come closer to the zona radiata. The effect of this is to produce in radial 

 sections through the micropyle the appearance of an immense funnel- 

 shaped depression in the whole capsular layer (Fig. 24). But the ap- 

 pearance is misleading ; there is no such broad depression ; the granulosa 

 cells of this region extend outward beyond their nuclei until they reach 

 the theca folliculi at the same level that the neighboring cells do. The 

 thickness of the capsular layer is therefore not changed in the vicinity 

 of the micropyle, and the theca folliculi does not bend inward, but 

 stretches over this region with a uniform curvature. The granulosa 



