MUSEUM OF COMPARATIVE ZOOLOGY. 103 



discover if such a passage took place, and particularly emphasized the 

 fact that the orifice of the micropyle is of exactly the same size as the 

 spermatozoon. 



These discoveries were soon (1855) confirmed by Leuckart ('55, 

 pp. 257-264) and Reichert ('56, pp. 83, 84, 98-104, Taf. IV. Figs. 1-4) 

 on the Continent, and by Thomson ('59, p. [100]-[104]) in England. 

 Their observations established the fact of the existence of the micropyle 

 in numerous fishes, and under several modifications of form. Ransom 

 had given a fairly accurate account of the structure of the micropylar 

 region, but Reichert especially insisted upon the differences between an 

 invaginated portion of the membrane and a passage through the latter 

 in the case of cyprinoids. He distinguished three regions, — an ap- 

 proach (Eingang), a fundus, and a neck or cylindrical canal, the length 

 of which was diminished from what it would otherwise have been by a 

 reduction in the thickness of the membrane to one third its normal 

 dimension. 



It was, however, the interest in fertilization stimulated by Newport's 

 researches on the impregnation of the ovum in Amphibia, and by Keber's 

 paper, "De introitu spermatozoorum in ovula," etc., Konigsberg, 1853, 

 that gave paramount importance to these discoveries, and attracted 

 general attention to them. 



Perhaps it is not surprising, in view of this fact, that the ovarian 

 egg was less studied, and that the relation of the micropyle to the gran- 

 ulosa cells in its vicinity was not especially examined ; and yet those 

 observers who concerned themselves with the questions relating to the 

 origin of the different egg envelopes must have been very near to inquir- 

 ing what share the granulosa had in producing so remarkable a modifi- 

 cation in the egg membranes. Kolliker ('58, p. 92), although only 

 incidentally making observations on the micropyle, established the fact 

 of its existence in a large number of cases. He regarded it simply as an 

 enlarged radial pore of the secondary vitelline membrane (zona), which 

 might be produced, he thought, by a process of resorption. 



Several subsequent writers have concerned themselves only with ques- 

 tions relating to the form and position of the micropyle, and its probable 

 function. Thus Buchholz ('63, p. 72) compared the micropyle in Os- 

 merus eperlanus to a crater the floor of which is closed except for a mi- 

 nute canal in the middle of it, which traverses the thickness of the wall ; 

 Ransom ('68), besides adding some unimportant details to his earlier 

 description of Gasterosteus, described briefly the micropyle in a large 

 number of other (fresh-water) fishes, claiming that it always terminated 



