118 BULLETIN OF THE 



the micropylar funnel ; and finally, it was described more fully for 

 Myxine by Cunningham. Eigenmann has found the same structure in 

 a number of bony fishes. 



32. The micropylar cell has never before been recognized. Eigen- 

 mann has now found it in a number of osseous fishes, — Perca, Pygos- 

 teus, Esox, etc. I believe it may fairly be assumed to exist in the 

 greater number of those fish eggs which possess a micropyle, and that it 

 has an important function in connection with the formation of the micro- 

 pyle or the fertilization of the egg. 



33. I have made the following suggestions as to the possible func- 

 tions and history of the micropylar apparatus : The micropyle, being 

 evidently a provision for the fertilization of the ovum, may have its 

 present structure as the result of two to some extent conflicting tenden- 

 cies ; one induced by the advantages of protection to the egg, the other 

 by the necessity of some provision for the penetration of the fertilizing 

 element. But the best protection is not compatible with penetrability 

 of the membrane at all points. Any reduction in the extent of the 

 penetrable surface would be favorable to protection. An optimum con- 

 dition would be reached when the penetrable area is reduced to a mini- 

 mum, and that is the diameter of the head of a spermatozoon. 



The funnel may be a partial compensation for such reduction. 



The micropylar plug may mechanically determine the presence and 

 form of a funnel. 



The micropylar cell may serve to form the canal by resorption, or to 

 prevent the occlusion of the canal by less penetrable matter at the time 

 of oviposition. 



Cambridge, April 7, 1889. 



