342 KOREN AND DANIELSSEN ON THE 



contains a transparent, pellucid, viscous liquid, like the white of 

 egg — investing a mass of ova (60 or more) . 



A number of the ova were placed under the microscope, after 

 freeing them from the viscous humour in which they had been 

 enclosed, and we saw that they possessed a delicate chorion, a 

 vitelline membrane, and a yelk consisting of a liquid, with many 

 contained granules. We were unable to distinguish either ger- 

 minal vesicle or spot. Each ovum was 0*194 millim. in dia- 

 meter. 



After some days had elapsed, we opened another capsule, and 

 observed, in the greater number of ova, the commencement 

 of a cleavage which appeared to be altogether irregular. In 

 fact, the number of spheres indicated by this cleavage was very 

 variable; and some of the ova, which, we may add, were all 

 provided with a chorion, had assumed an ovoid form (figs. 3, 4, 

 5, 6, T, 8, 9). The cleavage masses were all dark, and unpro- 

 vided with any nucleus. 



M. Nordmann has been equally unable to observe any nucleus 

 in Tergipes, Rissoa, or Littorina, The clear body which MM. 

 Van Beneden, Nordmann, H. Rathke, F. Miiller, Loven, and 

 other authors, have seen passing from the interior of the vitellus 

 to its surface (to which F. Miiller and Loven attribute the power 

 of determining the cleavage), has not appeared in the ova we are 

 describing, although we have taken great pains to look for it*. 



Some days later we examined many other capsules. The 

 viscous albuminous humour had undergone no appreciable 

 change. However, the ova were not so scattered as before, and 

 had approached one another. Examining them microscopically, 

 we observed that some had undergone no division ; others had 

 remained in a state of incipient division, — while around these 

 imperfectly developed ova there were a great number of others 

 in which division was more advanced. We see then, in this 

 case, that the ova have a disposition to collect together, and that 

 although enclosed in the same capsule, they exhibited a great 

 difference in the extent to which the cleavage process had taken 



* In a very recently published Appendix to this Memoir (Supplement til 

 Pectinibranchiernes Udviklings-historie, af J. Koren og D. C. Danielssen), llie 

 authors give an account of new observations on this point in Buccinum unda- 

 turn. In examining the youngest ova they have seen the clear (oily) body pass 

 out, and they describe, at length, the mode in which this takes place. 



