Development of the Pectinibranchiata, 355 



traces of vitelline molecules. The little body of which we are 

 speaking was first observed by M. Carus, and subsequently by 

 MM. Dumortier, Pouchet, Van Beneden, Bischoff, F. Miiller, 

 Nordmann, Vogt, Rathke, Kolliker, Reichert, Leydig, Loven, 

 and many others. Some of these authors take it for the pro- 

 jected germinal vesicle, others for the germinal spot, and others 

 again for a drop of exuded vitelline liquid. Like M. Loven, 

 we formerly regarded it as the germinal spot, but new observa- 

 tions have caused us to change our opinion, so that we now 

 agree with Eathke, Leydig, and Leuckart. Another question, 

 which has greatly attracted the attention of naturalists, is to 

 ascertain whether this body has anything to do with segmen- 

 tation. There is much difference of opinion upon this point 

 amongst authors. Rathke, Pouchet, Reichert and Leydig en- 

 tirely deny any such connexion. F. Miiller, Nordmann, and 

 Loven believe that this body shows the direction in which the 

 segmentation takes place. As most of the eggs of Buccinum 

 undatum do not undergo segmentation, and in the small number 

 which pass through the stages of this process this body is pushed 

 out of the egg before segmentation commences, it is clear that 

 we cannot speak of any relation between the latter and the body 

 pushed out. Soon after this little body has escaped from the 

 eggs, we see that the latter begin to agglomerate. The humour, 

 which was previously thick and viscous, then becomes more 

 liquid, so that there is no longer any difficulty in getting out 

 the contents of the capsules. The chorion has already begun 

 to detach itself in most of the eggs, forming a mass in the 

 humour. 



Some days afterwards, the act of conglomeration is completed ; 

 the eggs appear to be agglomerated at the bottom of the cap- 

 sule. The viscous humour has become perfectly fluid, like water, 

 and round the agglomerated eggs we see a greyish, finely granu- 

 lar, semitransparent mass, which assists in joining the eggs to- 

 gether (PI. XVI. fig. 1 a). The chorion is redissolved in most of 

 the eggs. In a little while we observe a group in the conglo- 

 merate formed by the whole of the eggs, — a larger or smaller 

 number of eggs appearing to be wrapped up in a transparent 

 veil formed by a viscous and finely granular humour exuded 

 from the eggs. This humour contracts by degrees, and forms 

 a very delicate membrane, which separates the group more and 

 more from what surrounds it. A group of this kind, when 

 recently formed, has much resemblance to a heap of balls placed 

 one upon the other (fig. I b). The exudation of the finely 

 granular humour continues, which enlarges the membrane, prin- 

 cipally at the upper part, the narrowest part of the group. We 

 also perceive slight contractions in the membranous envelope, 



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