176 MR. NEWPORT ON THE IMPREGNATION OF 



the upper portion of the yelk, and which diminish in intensity of colour from brown 

 or black at the circumference to a leaden or grey in the centre ; the other, which 

 forms the inferior portion, consisting of cells that become lighter-coloured as they 

 approach the surface. The whole form a mass of nucleated cells of nearly uniform 

 size, closely aggregated together. In the interior of the yelk, amidst the dark- 

 coloured cells, and much more near the surface of the dark than that of the white por- 

 tion of the ovum, I was surprised to find the germinal vesicle still entire (fig. 6), and 

 of a somewhat oval, lenticular form, although irregularly compressed by the contrac- 

 tion of the whole egg in the spirit. It was of a dense white colour, and opake, from 

 the action of the spirit, and was in striking contrast to the dark cells of the yelk, 

 which adhered to its surface, and amidst which it lay imbedded like the kernel in a 

 peach or apricot. On the surface of the black portion of the yelk was a minute 

 orifice, already noticed by PREVOST and DUMAS*, the outlet of a canal that passes 

 through this portion of the yelk to the germinal vesicle in its interior (fig. 6). This 

 I believe to be the result of the yelk cells having only imperfectly closed around 

 the germinal vesicle. It is however of some consequence in the future development 

 of the ovum, as it is in this canal that the cleavage of the yelk is commenced. The 

 vitelline membrane was already formed, but I could not discover any orifice or per- 

 foration in it, either corresponding to the canal in the yelk, or to any other part of 

 the surface. It is not possible to mistake the germinal vesicle for any portion of the 

 lighter substance of the yelk, first, from the fact that the vesicle at this period is of 

 an intense, opake, white colour, very different from that of the yelk substance, 

 next, from its being completely isolated from the lighter, and imbedded in the dark 

 substance, and lastly, from its being still invested with a distinct envelope. On re- 

 moving the vesicle, and examining it separately, first, as taken from the yelk, without 

 crushing it, and next by gentle compression, and with the highest powers of the 

 microscope, the interior was seen to be filled with secondary cells. Each of these, 

 formed by a distinct envelope, appeared to contain other, or tertiary cells, and strongly 

 reminded me of the developmental cells of the spermatozoa in the male organs, since 

 these again seemed to contain granules, or quaternary cells. In the midst of the 

 secondary cells I was able to distinguish, in the centre of the germinal vesicle, in some 

 specimens, one or two cells of larger size than the rest, and which I regarded as the 

 remains of the germinal spot, or central nucleus. In those ova which, from their size 

 and general appearance, seemed to be the most mature, the peripheral series of cells 

 within the germinal vesicle were of smaller diameter than those nearer to the centre, 

 as if the earlier developed secondary cells had disappeared and liberated their con- 

 tents. The cells of the dark portion of the yelk that adhered to the germinal vesicle 

 were also nucleated, but were of much smaller size than the peripheral cells of this 

 body. I must remark, however, that saving the fact noticed, of having seen in some 

 vesicles one or two cells near the centre of larger size than the rest, I have not been 



* Loc. cit, torn. ii. p. 104. 



