Fecundation of the Ovum, 301 



creases in size and acquires a granular consistence ; it afterwards 

 becomes the vitellus of the egg. Its surface condenses by 

 degrees into a membrane, the vitelUne membrane (cortical mem- 

 brane of Baer), and this at a time when the mass of the vitellus 

 still adheres to the stroma of the ovary (or rather to the ovarian 

 vesicle) by a tolerably broad base. But this base goes on nar- 

 rowing more and more, whilst the vitelline membrane continues 

 its formation, until the ovum at last only adheres to the stroma 

 of the ovary by a short peduncle like a neck. A transparent 

 liquid is then formed between the vitellus and the membrane, 

 and the peduncle is detached from the ovary. This point of 

 dehiscence is the micropyle of the Naiades. 



Leuckart is not the only zoologist who had pointed out the 

 micropyle before Keber. In 1850, J. Miiller described a canal 

 traversing the external envelope of the ova of certain Holothurice, 

 particularly Thyone fusus and Holothuria tubulosa^ ; in 1851 he 

 indicated a similar structure in the genus Ophiothrixf. In 1852 

 his son Max Miiller described the micropyle in the egg of Stern- 

 aspis thalassoidesX. All these discoveries had preceded that of 

 Keber, but they had not led their authors to a theory of fecun- 

 dation, although J. Miiller says § — " The comparison of this canal 

 with the micropyle of the ovule of the Phanerogamous plants 

 presents itself so naturally to the mind, that I could not avoid 

 mentioning it here;^' and Leuckart ||, in mentioning the micro- 

 pyle in the Naiades, adds — " We might almost suppose that this 

 singular structure has a certain relation with the act of gene- 

 ration.^' According to J. Miiller the micropyles of the ova of the 

 HolothuricE are in the cortical membrane (Schalenhaut) , besides 

 which there is also a vitelline membrane. Leuckart^ positively 

 denies the existence of the latter, and gives the name of " vitelline 

 membrane " to that which contains the micropyle. In other re- 

 spects he describes the formation of the micropyle here exactly 

 as in the Naiades ; — it is the remainder of the peduncle which 

 attached the ovum to the stroma of the ovary. The formation 

 of the peduncle always depends upon that of the membrane, and 

 as this does not exist at the point of attachment itself, it is 

 clear that there always remains an opening at the place of the 

 peduncle. This is the micropyle. 



But Loven appears to have been the first to perceive the mi- 

 cropyle, for, in a work of his v/hich dates as far back as the year 



* Metamorphose der Echinoderraen, 4te Abhandl. 1850. 



t Monatsbericht der BerHner Akad. 1851. 



X De Vermibus quibusdam maritimis. Diss, inaug. Berlin, 1852. 



§ Ueber die Metamorphosen der Echinoderraen, 4te Abhandl. p. 42. 



II Article Zeugung in Wagner's Handworterbuch der Physiol, iv. p. 801. 



•[[ Zusatz zu Bischoff's Widerlegung. 



