116 BULLETIN OF THE 



13. Each villus is composed of three parts, — head, stalk, and roots. 

 The roots project into the pore-canals of the zona. 



14. The zona presents the usual structure of that memhrane in bony 

 fishes. The pore-canals are slightly enlarged and spiral at their periph- 

 eral ends. 



15. The egg of Lepidosteus has a single micropyle, but it has been 

 overlooked by previous observers. 



16. The micro pylar apparatus embraces a funnel and a canal. The 

 funnel results from an infolding and a reduction in thickness of both the 

 villous layer and the zona radiata. The micropylar canal is a narrow pas- 

 sage of uniform calibre (2 fx) and circular cross section, through the thin- 

 nest part of the two membranes, namely, at the bottom of the funnel. 



1 7. The granulosa of the mature ovarian egg consists of a single layer 

 of polygonal cells, except in the region of the micropylar funnel, where it 

 forms a plug of cells completely filling the funnel. 



18. The membrana propria of the theca folliculi is not infolded in the 

 region of the micropylar funnel. 



19. A single large granulosa cell, the "micropylar cell," forms the 

 apex of the plug, and occupies the bottom of the funnel. 



20. The villous layer is formed before the zona radiata. It first 

 appears at the surface of the yolk in eggs about 0.4 mm. in diameter, 

 and reaches one third its maximum thickness a year before the egg ma- 

 tures. It is produced by the ovum, not by the granulosa cells. 



21. The number of the villi is not increased during the growth of the 

 villous layer. 



22. The zona radiata is likewise the product of the ovum, and its 

 formation requires less than twelve months. 



23. The name " capsule " should not be used for the zona radiata ; it 

 ought to be restricted to membranes outside the zona, which, like that 

 of the perch, are the product of the granulosa. 



24. An egg membrane comparable structurally and genetically with 

 the zona radiata of bony fishes is to be found in representatives of all 

 the groups of fishes except Amphioxus. It is fugitive in selachians and 

 Lepidosiren, and probably in viviparous teleosts. The zona is produced 

 by the ovum, not by the follicular cells, and is traversed in all cases by 



