ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 645 



complex, and wholly typical of the Acmaaida?. From each plearal 

 ganglion, there are two principal pallial nerves, which reach a circum- 

 pallial nerve completely encircling the animal near the mantle edge. 

 This nerve is ganglionic, and supplies the finer nerves to the mantle. 



Anatomy of Corolla (Cymbuliopsis) spectabilis.* — H. Heath and 

 M. H. Spaulding give an account of the anatomy of this Pteropod. 

 There is a symmetrical proboscis, comparatively thin and broad, and 

 free from the fin for nearly half of its length. Its free margins form 

 a groove of richly ciliated tall columnar cells profusely innervated. It 

 appears to function as an organ of special sense, and as a contrivance 

 for collecting and directing food to the mouth. The foot or fin, 

 modified into a swimming organ, is operated by two systems of muscle 

 bands. Along its margin there are multitudes of sense-organs, appa- 

 rently light percipient structures, the details of whose development are 

 remarkable. There are no cephalic eyes. There appear to be no data 

 discovered by the authors to enable them to decide whether the species 

 is truly hermaphrodite, whether the penis has entirely disappeared, 

 whether there is progressive hermaphroditism, or whether the males are 

 still undiscovered. 



5. LamellibrancMata. 



The Formation of Pearls.f — W. A. Herdman sums up the various 

 points in the problem of pearl-formation. In particular he criticises 

 Jameson's views as to the mode of origin of the epithelial sac which 

 encloses the larval parasite, and which secretes from its cellular walls 

 layer after layer of nacreous material so as to form a pearl. He thinks 

 there can be little or no doubt that the cells of the pearl sac are directly 

 and genetically connected with the cells on the outside on the mantle. 

 He has found also that the evidence for Jameson's view that the 

 mussels are infected by parasites from Tapes and Cardium, is very far 

 from sufficient. There are two points in particular which require 

 clearing up : the exact details of formation of the pearl-producing 

 epithelial sac when deeply placed in the tissues, and the complete life- 

 history of the parasite inside the sac. 



Evolution of Pecten.J — C. B. Davenport has made a quantitative 

 study of Pecten opercular is from three separate localities of the British 

 Isles, viz. Firth of Forth, Irish Sea, and English Channel. The general 

 conclusions drawn from his results are that the three lots are measurably 

 unlike in size, proportions, and average number of rays. The geo- 

 graphical extremes are the biological extremes also. The evidence from 

 the shells examined bears upon De Vries' law of mutation. Where the 

 environmental conditions of the isolated form units are similar, the 

 differences met with are easily accounted for on the assumption of 

 mutations which are preserved. Where, on the other hand, the en- 

 vironmental conditions are dissimilar, it is obvious that they must pro- 

 duce a change either through their direct and definite action or possibly 



* Zool. Jahrb. xx. (1904) pp. 67-80 (1 pi.). 



t Rep. Lancashire Sea Fisheries Lab., 1901, pp. 88-97. 



X Proc. Amer. Acad. Sci., sxxix. (1903) pp. 123-59. 



Dec. 21st, 1904 2 y 



