THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY. 



[SECOND SERIES.] 

 No. 114. JUNE 1857. 



XXXIII. — Besearches on the Development of the Pectinihranchiata. 

 By J. EoREN and D. C. Danielssen. 



[Concluded from p. 366.] 



Pwpura lapilhs [Buccinum], Linn. 



The capsules in which the eggs are enclosed somewhat re- 

 semble a little bottle, of which the convex bottom would be 

 turned upwards, and the very slender neck directed downwards. 

 It is by the lower extremity that they are fixed either to stones 

 or other bodies. Each capsule is hermetically closed, and filled 

 with a viscous fluid, as transparent as water, and resembling 

 white of egg, containing a multitude of eggs (from 500 to 600 

 or even more). The eggs are of a globular form, furnished with 

 a delicate chorion, a vitelline membrane, and a vitellus consist- 

 ing of a fluid containing small granules. Amongst the smallest 

 of these granules there are, as in Buccinum, a quantity which are 

 oval, and refract light very strongly. We could not distinguish 

 either a germinal vesicle or a germinal spot. After an interval 

 of several days, a commencement of segmentation appeared 

 in the eggs, which divided first into 2 and then into 4 spheres 

 of segmentation. These stages passed pretty regularly. But 

 then a great irregularity made its appearance in the segmenta- 

 tion : we soon saw some of the spheres divide, while the others 

 remained intact ; in others, 4 small spheres were formed between 

 the 4 large ones; and others, again, had become divided into 12 

 or 18 irregular spheres. It was not rare to find eggs which had 

 not yet undergone segmentation ; some were also found in which 

 the segmentation had progressed a little way, and in which the 

 chorion was not yet ruptured. In our first memoir * we have given 

 figures of these eggs, and new observations have proved their 

 correctness. In this way we observed a number of eggs, which, 



* This memoir will be found translated in the Scientific Memoirs, new 

 series, Nat. Hist, division, p. 330, plates 10, 11 & 12. 



Ami. ^ Mag. N. Hist. Ser. 2. Vol. xix. 28 



