24 SUaiMARY OF CURRENT RESEARCHES RELATING TO 



fully, and he concludes by pointing out that two tissues, one fibrous 

 and one hyaliue cartilage, are to be made out in the neck-car- 

 tilage ; the former gives rise to an internal meshwork, such as is 

 again to be detected in the aptychus. A supporting mass of calcified 

 tissue contains a hard body which has taken the place of the macerated 

 hyaline cartilage, comparable to that found by Hasse in the fossil 

 vertebrae of Squatina, where calcified layers of cartilage alternate 

 with the hyaline form. 



Olfactory Organ of Terrestrial Pulmonate Gastropoda .*— The 

 first object of Dr. D. Sochaczewer seems to be to decide between the 

 claims of the tentacles, the organ of Semper, and the pedal gland, to be 

 regarded as the olfactory organ of these Gastropods. The first of 

 these parts contains a large ganglion each, Avhence five fibres radiate 

 into the investing epithelium and give rise to terminal knobs, endowed, 

 apparently, with a sensory function. It is not, however, the opinion 

 of all naturalists that these nervous parts are olfactory organs, for 

 some, like Linnaeus, have regarded them as having a tactile function ; 

 and this view would appear to be supported by the rapidity with which 

 these processes contract when they come in contact with any foreign 

 body. 



The original experiments performed by the author in order to 

 arrive at a determination of the question were of the following cha- 

 racter : — An example of Helix pomatia had its tentacles cut off, and, 

 after the healing process was completed, the snail was placed in the 

 centre of a flat plate, the edge of which was smeared with oil of tur- 

 pentine. The movements of the snail were very slow and uncertain. 

 When it approached the edge of the plate it behaved itself exactly as 

 did a snail in which the tentacles were completely uninjured, returning 

 at last to the middle of the plate and withdrawing itself into its shell. 

 This and similar experiments seem to show that the tentacles are not 

 the seat of the olfactory sense. 



The second organ — the organ of Semper — is next considered. 

 This structure has received its name from the fact that it was dis- 

 covered by Professor Semper (1856). Small in Helix, Avion, and 

 Lymnceus, it is especially well developed in Limax. Here it has the 

 form of four or five glandular lobate processes, which are set at the 

 sides of the mouth. Each lobe is notched on its margin, and from this 

 notch there sometimes extends a shallow groove over the whole of the 

 lobe. The lobe itself has, owing to the presence of a number of slits, 

 the appearance of a three or four-toothed comb, connected together 

 by the complete marginal portion. Semper reported that this organ 

 was very richly supplied with nerves, and, consequently, regarded it as 

 a sensory organ. Dr. Sochaczewer found four fine fibres, of which 

 the two median were recognized to be muscular in character, while the 

 lateral branches are the proper nervi labiales, which only give off on 

 either side a fine nerve-branch to the glandular masses of Semper's 

 organ. The cells of the constituent lobes resemble, as Semper him- 

 self pointed out, the glandular cells of the salivary organs, and still 



* Zeitbchr. -wiss. Zool., xxxv. (1880) pp. 30-4G (1 pi;). 



