430 MisceUaneous. 



against Sir Wyville Thomson's course of action, and denounce it as 

 unjust and unpatriotic; and in this protest 1 am joined, as will be 

 proved shortly, by nearly every scientific man with whom I have 

 communicated. I doubt whether Sir Wyville Thomson is justified 

 by the instructions of the Grovernment reg-arding the disposal of the 

 Collections ; but this question will be settled when the correspond- 

 ence is moved for in the " House." In conclusion, I wish, in my 

 own name and on behalf of those naturalists who act with me, to 

 express our admiration of the laboiirs of the distinguished men who 

 ai'e mentioned by Mr. A. Agassiz, and our thorough appreciation of 

 his own genius and liberality. "VVe can only regret that these gen- 

 tlemen have been placed, by no fault of their own, in a position 

 so invidious that they can hardly occupy it conscientiously. 



Yours, &c., 



P. MAKTrcf Duncan, F.R.S., 

 April 20, 1877. Pres. Geol. Soc. 



On the Modifications undergone bif the Ovum of the Phanerocarjryal 

 Medusae before Fecundation. By M. A. Giard. 



"VVe shall take as a type the ovum of Rhizostoma Cuvieri. This 

 fine Medusa is thrown up in great abundance, during the whole 

 autumn, on the beach at Wimereux, together with Chrysaora hyo- 

 scella and some other Acalephs. 



The smallest ova taken from the ovary are formed of a trans- 

 parent vitellus containing a germinal vesicle and a nucleolus. We 

 do not yet recognize in them any enveloping membrane. As the 

 ovum increases in size its transparency diminishes ; the vitellus 

 becomes charged with deutoplasm, and the germinal vesicle less 

 easy to appreciate ; at the same time a very delicate vitelline mem- 

 brane, closely applied to the vitellus, may be distinguished at the 

 periphery. In a later stage the ovum presents at its periphery a 

 series of spherules equally distributed over its whole surface, filled 

 with a perfectly hyaline substance, and separated from the external 

 membrane by a thin layer of granular protoplasm, identical with 

 that which occupies the centre and covers the germinal vesicle. An 

 optical section of the ovum may then be roughly compared to 

 that of a young stem of a plant at the moment of the appearance 

 of the first circle of vascular bundles which divide the parenchyma 

 into three parts — one central, another peripheral, and the third 

 radial (uniting the two former). The hyaline spherules increase 

 rapidly, become tangential to one another, at the same time that 

 they reach the vitelline membrane. Under a low power it appears 

 as if the vitellus were surrounded by a layer of cells which project, 

 rectangularly at its periphery. Under a higher power it is seen 

 that the central granular protoplasmic mass is united to the vitel- 

 line membrane by a multitude of little columns, widened at their 

 two extremities, like the columns formed in a cavern bj^ the union 

 of the stalactites and stalagmites. These little columns are foi-med 

 b}- a less granular protoplasm than that of the centre of the ovum. 



