ZOOLOGY AND BOTANY, MICROSCOPY, ETC. .'303 



Nepionic Stage in the Gastropods.* — H. L. Kesteven discusses 

 different types of transition from embryonic to neanic shell structure, 

 as seen in Melo in dims, Lotorium abbotti, and Triphora. He arrives at 

 the following definition of the nepionic stage, "That stage during 

 which the velum undergoes degeneration and disappears," and main- 

 tains that " where no varix is thrown up at the conclusion of the 

 embryonic shell, no conchylaceous record of the nepionic stage has 

 been left by the mollusc." He admits that the pseudoprotoconch may 

 be the homologue of the embryonic varix, and that it is likely that 

 some pseudoprotoconchs are nepionic. 



Inverse Symmetry in G-astropods.f — E. Gr. Conklin finds that 

 inverse symmetry may be traced from the first cleavage of the egg, 

 which in such cases is found to be inverse, and he considers that this 

 must be preceded by an inverse organisation of the unsegmented egg. 

 No inverse organisation can be detected in the ovarian eggs of sinistral 

 snails, and it is, therefore, probable that it arises about the time of the 

 maturation or fertilisation of the egg. 



Maturation and Fertilisation in Cymbulia Peronii.J — A.Nekrassoff 

 describes the phenomena observed by him in the maturation and fertili- 

 sation of this species. In particular his results do not support Boveri's 

 view of the origin of the " segmentation centrosomes." His conclusion 

 is that they arise de novo. There is no connection, he thinks, between 

 them and the egg centrosome which has disappeared much earlier, nor 

 can they owe their origin to the sperm. " They originate through the 

 mutual relations of the nucleus and the plasma." 



5. Lamellibranchiata. 



Secretion of Pearls.§ — R. Dubois has made for years a study of 

 pearl-formation in Margaritana, Unio, Anodonta, Pinna, 3/gtilus, and 

 Morgaritifera, and formulates four conclusions. The formation of the 

 pearl and of the nacre cannot be compared to an ordinary simple 

 secretion. The organic basis and the carbonate of lime cannot be 

 secreted by the same element. The apparently diverse structures of 

 pearls are readily explicable as due to the passage of migratory calci- 

 ferons elements through a fenestrated epithelium secreting the con- 

 chyolin. The nacre, though the result Qf rougher work than the fine 

 pearl, is produced by essentially the same mechanism. Some details of 

 the complex secretory process are given. 



Detection of Pearls by means of X-Rays.|| — Raphael Dubois has 

 been successful in detecting the presence of pearls, even of small size, 

 by means of the X-rays. If this method is readily practicable — and 

 it has been used in Ceylon — it will save much useless destruction of 

 pearl-oysters, etc., and will also economise time. 



* Proc. Linu. Soc, N.S.Wales, xxviii. (1903) pp. 443-52. 



t Proc Acad. Nat. Sci. Philadelphia, 1903, p. 753. 



X Anat. Anzeig., xxiv. (1904) pp. 119-27. 



§ Comptes Rendus, cxxxviii. (1904) pp. 710-2. 



|| Tom. cit. pp., 301-2. 



Y i 



