304 M. E. Claparede on the Theory of the 



more value, — he remarks, incidentally, that sometimes the pe- 

 duncle remains widely open, and continues to project externally 

 even after the ovum is surrounded with albumen, so that there 

 remains a means of communication between the vitellus and the 

 external world. We may, perhaps, observes Meissner, compare 

 this structure of the ovum with the micropyle observed by 

 Leuckart, J. Miiller and Keber in the Naiades and Holothurice. 



However, a few months afterwards, a new paper by Meissner* 

 made its appearance, in which he not only confirms the discovery 

 of a micropyle, but also that of the penetration of the sperma- 

 tozoa into the ova of veiy diflFerent animals. The greater part 

 of this work relates to the Ascaris mystax of the Cat, the same 

 which had formed the subject of Nelson^s observations; but 

 he mentions several other species of Ascarides, a Strongylus, 

 some Lumbrici, and the Rabbit. INIeissner describes the forma- 

 tion of the spermatozoa and ova in the Ascarides as exactly the 

 same as in Mermis albicans. The formation of the micropyle is 

 due to the same circumstance. Nevertheless, he does not 

 venture to regard this as a general type of development, for he 

 has himself ascertained that it has exceptions. Thus, in Stron- 

 gylus armatus the raphe, instead of being an apparent axis 

 formed by the succession of germ-cells, is a true raphe. In this 

 worm, the ova are a kind of diverticula of a pear-shape, sus- 

 pended from a single vessel or vitelligenous tube, representing 

 the germ-cells. 



Nelson had seen the spermatozoa of Ascaris mystax penetrate 

 into the ovum at all parts of its surface, and especially at one 

 angle of this triangular ovum, to which he gives the name of 

 the broken edge. Aleissner shows, from the mode of formation 

 of these ova, that they possess a vitelline membrane with a 

 single aperture, through which he has himself repeatedly seen 

 one or more spermatozoa penetrate. This opening, the micro- 

 pyle, coincides exactly in position with the broken edge of Nelson. 

 The cases in which the English anatomist thought he saw the 

 penetration take place at other points, are probably to be attri- 

 buted to errors. The spermatozoa observed by Meissner also 

 coincide with the spermatic cells of Nelson, which Bischofi" de- 

 clared to be nothing but epithelial conules. Fecundation takes 

 place at the moment when the ova ai'rive in the portion of the 

 tube or sexual vessel which has already been denominated the 

 albuminogene. The number of spermatozoa which penetrate 

 by the micropyle is vei'y variable, for Meissner has seen as many 

 as ten in the interior of a single ovum. \Vhen fecundation is 



* Beobachtungen iiber das Eindringen der Samenelemente in den Dotter. 

 Zeitschr. fiir wiss. Zoologie, vi. Sept. 1854. 



