ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 39 



In regard to the development of the ovum, an interesting point is 

 the growth after fertilisation of little papillae on the surface of the egg, 

 to form a complete spiny covering, which degenerates again and is cast 

 off within the oviduct. These spiny processes have been described as 

 " pseudopod-like," and as being retracted later, but the author regards 

 them as a protection against multiple fertilisation, and suggests that the 

 fact that it takes this form instead of that of a mere skin-thickening 

 may be due to " phylogenetic reminiscence." 



In addition to a beautiful series of photographs showing the succes- 

 sive stages in the process of pairing, the paper is illustrated with drawings 

 of all the internal parts, in all phases of rest and activity, extrusion and 

 retraction. These were obtained by killing and immediately fixing 

 snails in process of copulation. 



Origin of the Nematocysts of Eolidiae.* — L. Cuenot gives strong- 

 reasons for concluding that the nematocysts of the cnidophore-sacs of 

 Eolids do not really belong to these animals. They are not made by the 

 cells which contain them. They come from the Ccelentera on which 

 the Nudibranchs feed. 



He argues that the nematocysts pass intact through the digestive 

 tract and enter the hepatic diverticula of the papilla? ; they reach the 

 cnidophore-sacs and enter the " nematophagous " cells, where they are 

 arranged so that the end by which discharge is effected is turned towards 

 the free surface of the cell. 



Cuenot removed the cnidophore-sacs from some Eolids, fed some 

 with a species of sea-anemone, and left the others fasting. In both 

 cases the sacs were rapidly regenerated, growing in the same way as in 

 normal development. The well-nourished Eolids had their nemato- 

 phagous cells equipped with the nematocvsts of the sea-anemone, but the 

 fasting Eolids showed no nematocysts. 



Eolids do not seem to profit much by their borrowed nematocysts, 

 which are rendered less effective by their position within an internal sac. 

 It is true that some fishes seem to regard Eolids as unpalatable, but it 

 does not appear that this is because of the nematocysts. 



Development of Fulgur.f — E. G-. Conklin gives an account of the 

 development of Fulgur, devoting particular attention to the influence of 

 the large mass of yolk. The cleavage of the egg of Fulgur is, cell for 

 cell, like that of Crejiidula up to the 56-GO cell stage, the only difference 

 being in the relative sizes of the macromeres in these two genera. In 

 later cleavages many more ectoderm-cells are formed in Fulgur than in 

 Crepidula. The overgrowth of the yolk is very peculiar. By very great 

 extension of the anterior half of the blastoderm, while the posterior 

 half remains relatively fixed, all the organ bases are carried to the 

 posterior margin of the blastoderm, where they form a kind of germ- 

 ring. Subsequently the posterior margin also moves over the yolk, so 

 that the blastopore is finally formed at the vegetal pole. 



Before the extension of the anterior portion of the blastoderm an 

 apical invagination of ectoderm cells is formed, which eventually dis- 



* Arch. Zool. Exper., vi. (1907) pp. 73-102 (1 pi., 4 figs.). 



t Proc. Acad. Nat. Sci. Philadelphia, 1907, pp. 320-59 (G pis.). 



