MUSEUM OF COMPARATIVE ZOOLOGY. Ill 



The fact that Eigenmann ('90) has been unable to discover a micro- 

 pyle in the earlier stages of the formation of the egg membranes in fishes 

 may also point in the same direction. I would not wish, however, to 

 place too much weight upon such negative evidence ; it requires exten- 

 sive and indeed the most exhaustive examinations to make such" testi- 

 mony satisfactory. Especially am I compelled to this reserve, in view 

 of the fact that Cunningham ('86 a ) has found the micropylar apparatus 

 well developed at a relatively early stage in the formation of the zona 

 in the case of Myxine glutinosa ; but it will be observed that he says 

 (p. 61) : "This cellular projection is covered by a thin membrane continu- 

 ous with the vitelline membrane, and is not in immediate contact with the 

 germinal disk." An actual opening does not exist, therefore, at the time 

 of which he speaks. Although I have found in M. australis at an ap- 

 parently early stage in the development of the zona a deep infolding of 

 that membrane, as described above, still I have not satisfied myself in 

 the single specimen sectioned that there is an orifice through the mem- 

 brane at this stage of development. But on this observation I would 

 not care to speculate were it not confirmed by Cunningham's studies 

 on more extensive and I presume histologically more favorable material, 

 for I know how easily one may be deceived as to the existence of so 

 minute a structure as that with which we have to deal. 



The facts which I have given above do have a certain weight with me 

 as rendering it possible that in Myxine at least the micropylar canal, in 

 the strict sense of the word, is not present until near the maturity of 

 the ovum, and that consequently it may be the function of the cell 

 nearest to the bottom of the funnel — the micropylar cell — to absorb 

 so much of the already formed membrane as is necessary to allow the 



anfangs nur kurz ist, spater mit dem Diekerwerden des Chorions und dem entspre- 

 chenden Zuriickweiuhen der Epithelschicht aber langer und langer wird." 



In his final paper, Korschelt ('87, p. [43] 223) suggests a method of reconciling 

 Leuckart's views with his own observations: "Die Beobachtung Leuckart's, nach 

 welcher die Mil: ropy lkanale sich nicht von Anfang an am Chorion finden sollen, 

 liesse sich vielleicht mit nnseren Befunden in Uebersinstimmnng bringen. Wir 

 erkannten in mehreren Fallen, dass die Masse des in der Bildung begriffenen 

 Chorions eine durchaus weiehe und plastische sein muss. Deshalb ware es leicht 

 denkbar, dass die Zellfortsatze, welclie die Kanale entstehen lassen, nicht von 

 Anfang der Bildung an vorhanden waren, sondern erst spater in die weiehe Masse 

 des jungen Chorions hinein entsendet wiirden. Dann wtirde es ein Stadium geben, 

 in welchem das Chorion eine ununterbrochene Oberflache besasse. Seine Ansicht, 

 das die Mikropylkanale an dem bereits gebildeten Chorion durch Resorption 

 entstehen sollen, diirfte Leuckart wohl aufgegeben haben, sobald er die Entste- 

 hungsweise der Porenkanale der Eischale kennen lernte." 



