110 



BULLETIN OF THE 



plug represents the same structure in Lepidosteus, and that conse- 

 quently the micropylar canal is to be found at the bottom of the 

 funnel-shaped infolding produced by the plug. 



4. Micropylar Cell. 



Although no other cases are yet known in which a single cell of 

 the follicular micropyle-plug is so evidently differentiated from its 

 neighbors, as in Lepidosteus, still it is clear from the results of Eigen- 

 mann's ('90) studies that the existence of such a specialized cell is not 

 uncommon. 



The most interesting question relative to the micropylar cell is that 

 of its physiological signification. 



That it sustains some intimate and constant relation to the micropyle 

 itself can scarcely be doubted. Perhaps its primary function is fulfilled 

 by serving as a source of passive resistance to the forming membranes 

 in the region of the micropyle — a kind of mould for them — during 

 the process of their formation, therefore a mechanical device for pro- 

 ducing a micropylar funnel. In that case it would doubtless often be 

 more than the single micropylar cell on which devolved the function ; it 

 would be rather that plug-like accumulation of granulosa cells, with the 

 micropylar cell at its apex, which attains such an extensive development 

 in Lepidosteus and some other cases. 



But the very fact that one cell is generally, if not always, differen- 

 tiated more than the rest, suggests that the function referred to may 

 not be the only one, — perhaps, indeed, not the primary one. There 

 are two other possible functions which are naturally suggested in this 

 connection. 



Concerning the first of these it may be said that it still remains to be 

 shown to what extent the micropylar canal and its funnel are the result 

 of an exclusively progressive process of development ; whether, in other 

 words, any part of this structure is produced by a process of resorption. 

 Such a process would not be without a parallel. At least Leuckart ('55, 

 pp. 108, 216, 247) has asserted in most positive terms that the micropyle 

 of certain insects' eggs is not to be found in the chorion from the very 

 beginning of its formation, but that it arises after the production of the 

 chorion by means of resorption, 1 



1 More recently, it is true, Korschelt ('84, pp. 421, 422) has shown that the 

 micropyle in Meconeraa varians is formed by a single cell, and he apparently leaves 

 no room for a process of resorption, since he says : " Die Entstehung des Canals ist 

 wohl so zu denken, dass die Zellen schon friihzeitig einen Fortsatz ausstrecken, der 



