183 M. E. Claparede on the Formation of the Egg 



line substance takes place from without, proceeds more cau- 

 tiously, and does not venture to decide in any way as to the 

 place of formation of the vitelline granules. We do not believe 

 that the vitelline granules can be formed by the longitudinal 

 processes, because free vitelline granules never occur between 

 the wall of the genital tube and the column of ova. Moreover, 

 the granules would have to penetrate first of all into the outer 

 granule-less layer of the yelk, if the deposition took place from 

 without ; but nothing of the kind is observed. It is not to be 

 doubted that in the upper part of the genital tube the granules 

 are formed all round the germinal vesicle ; but as soon as the 

 rhachis makes its appearance, it seems to us that this must 

 be considered as the place of formation of the vitelline granules. 

 It is (in Ascaris suilla) comparatively very broad and densely 

 filled with vitelline granules ; more densely, in fact, than 

 the eggs themselves. In the lower part of the vitellogene, at 

 the point where the eggs separate by constriction, the rhachis 

 disappears. What, then, has become of its contents ? They 

 have passed into the corresponding ova; and we believe that 

 every new vitelline granule that appears in an egg has come 

 over from the rhachis. This view does not differ much from 

 that of Meissner. In either ease, the vitelline granules are pro- 

 duced in the rhachis; but in the one case the rhachis is real, in 

 the other apparent. 



The question of the micropyle in the ova of the Ascarides is 

 one of great importance, as Meissner's theory of fecundation 

 entirely depends upon it. A micropyle, such as is described by 

 Meissner — that is to say, an aperture in a membrane — certainly 

 does not exist, as we cannot detect any true membrane. Meiss- 

 ner^s theory is not, indeed, compromised by this, as a fissure in 

 the external, denser, vitelline layer might very well perform the 

 function of a true micropyle. But we cannot admit the micro- 

 pyle even in this limited sense. The ovum gradually separates 

 itself from the rhachis by constriction, so that the bridge of 

 connexion between the two becomes thinner by degrees, and at 

 last disappears. There then remains no fissure in the outer 

 layer, but the place of the pretended micropyle is clothed, like 

 the rest of the egg, with this layer. 



The changes which the egg undergoes in the lower part of 

 the oviduct will be referred to hereafter, at the same time with 

 the fecundation. 



Amongst the Nematoidea in the vitellogene of which a rhachis 

 is to be met with, we shall also mention Cucullanus elegans. 

 Siebold, even in his ' Comparative Anatomy,^ places this worm 

 amongst those which have a rhachis in the vitellogene, but says 

 nothing further upon it. It must therefore appear strange that 



