ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 375 



organs and of the lateral organs of the abdomen of the Capitellidae was 

 noticed in the preliminary communication ; since then the author has 

 had the opportunity of examining preparations of the latter, and finds 

 that the likeness is very great. A detailed account is now given of the 

 histological characters of these bodies in Lamellibranchs, and it is shown 

 that in them, as in the Capitellidae, only one kind of cell is in contact 

 with the surface, and that the nuclei thereof are spindles. The character 

 of the epithelium and its connection with the nervous system justifies 

 the conclusion that the papillae found in the region of the anus are 

 sensory organs ; as they are provided with a number of long hairs, 

 which are set in motion by every current of water, their function would 

 appear to be that of perceiving movements in the surrounding medium. 

 They are, in other words, organs of the sixth sense. It is, indeed, 

 possible that they have also some power of olfactory perception, but it 

 cannot be that they have any tactile power. Their absence in the 

 Siphoniata seems to show that their chief duty is the perception of 

 movements in the water; in siphoniate forms sensory organs for the 

 perception of water-movements are placed at the end of the in-current 

 siphon. 



Turgescence in Lamellibranchs.* — M. A. Menegaux has made a 

 somewhat extended examination of the phenomena of the turgescence of 

 the foot in Lamellibranchs. He comes to the conclusion that, in all 

 those in which this organ is well developed, there is an orifice provided 

 with a sphincter muscle, and that this is wanting in the rest ; the inter- 

 vention of water is, therefore, not necessary to explain the enlargement. 

 A post-ventricular and muscular dilatation aid the heart in driving the 

 blood into the siphons, while two successive valves oppose the direct 

 return of the blood into the heart during the rapid contraction of the 

 siphons. 



Bevelopment of Oyster and Allied Genera.!— Mr. E. T. Jackson has 

 a preliminary paper on the later development of the oyster, with studies 

 of allied genera. He considers that the two valves of an adult oyster 

 are altogether homologous with the single valve of adult cephalous 

 Mollusca, for both originate from the preconchylian gland. As the 

 adult shell of the latter is termed a conch, the name dissoconch (double 

 shell) is suggested for that of adult Lamellibranchs, The form and 

 structure of the shell in the stages recognized by Eyder — prodissoconch, 

 silphologic (spat), and adult, are considered in detail. Mr. Jackson 

 directs attention to a striking peculiarity in the Ostreidse which he 

 thinks has escaped notice ; the two valves are as dissimilar as if they 

 belonged to distinct species. This is regarded as evidently a case of 

 inherited or acquired characteristics. 



Byssus of young of common Clam.f — Mr. J. A. Eyder has made 

 some observations on the byssus of the young of Mya arenaria. Sections 

 were prepared to determine if there was a byssus-gland in the foot ; these 

 were obtained by treatment with 1/2 per cent, chromic acid solution, 

 which was afterwards acidulated with nitric acid. In the sections of the 

 median region at the apex of the foot a median saccular depression, which 

 was undoubtedly the byssal gland, was detected. The presence of this 



* Comptes Kendus, cviii. (1889) pp. 361-4. 



t Proc. Boston Soc. Nat. Hist., xxiii. (1888) pp. 531-56 (4 pis.). 



j Amer. Natural., xxiii. (1889) pp. 65-7. 



2 D 2 



