316 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the optic ganglion in Aplysia, &c, the organs of Hancock, and the 

 systematic position of the group. 



Sensory Cells in Mouth-cavity of Helix* — Dr. H. Smidt adds a 

 brief note to his previous paper on this subject. From a comparison 

 of the "polype-cells" of the buccal cavity with the corresponding 

 sensory structures found on the large tentacles, he has found reason to 

 believe that the hair-like processes of the cells are capable of spon- 

 taneous movements, by means of which they escape the impact of 

 stimuli of too great force. 



Histology of Nervous System in Helix, f — Dr. H. Smidt has em- 

 ployed Golgi's method for the solution of the problem of the morpho- 

 logical value of certain cells in the nervous system of the snail, to which 

 he has given the name of companion-cells. He finds that in the case of 

 peripheral nerves these companion-cells are definitely connective-tissue 

 cells, and vary according to the nature of the structure they surround. 

 It is otherwise with the cells found in the radially arranged septa which 

 divide the great nerve-trunks and the commissures into three-sided 

 prisms. These have a system of fibrillas which recalls that of the glia- 

 cells of vertebrates, and may justly be called glia-cells. In the ganglia 

 of the snail, multipolar cells occur which are connected by transitional 

 forms with the glia-cells of the nerves, and which again recall the glia- 

 cells of vertebrate ganglia. These cells do not appear to send pro- 

 longations into the ganglion-cells, hut they cling very closely to them. 



Anatomy of Triboniophorus.J — Dr. Wilhelm Pfeiffer has studied 

 the structure of three specimens of this little-known genus. The speci- 

 mens were obtained from Brisbane, and proved to belong to a hitherto 

 undescribed species, named T. brisbanensis by the author. Among the 

 more remarkable characteristics are the following. There are only two 

 retractile tentacles, which bear the eyes and are moved by four posterior 

 retractors and two anterior retractors. The pulmonary chamber forms 

 a system of tubes which are surrounded on all sides by the blood of the 

 dorsal sinus, pulmonary vessels being absent. The ureter is complexly 

 coiled, and is ciliated in certain areas. In the middle of the dorsal 

 surface there is a shell-sac, which contains a calcareous rod and 

 possesses a glandular diverticulum. The organs of the pallial complex 

 are separated from the body-cavity by a muscular diaphragm, and 

 between diaphragm and dorsal body- wall there is a remarkable sense- 

 organ, apparently homologous with the osphradium of the Basommato- 

 phora. It is supplied by two stout nerves. The organs of the body- 

 cavity consist of the digestive system, the genital apparatus, and the 

 nervous system. The stomach is tubular, and is furnished with a 

 caecum, into which one of the three hepatic ducts opens. The paper 

 contains a table showing the relation of the new species to those pre- 

 viously described ; but the anatomy of the latter is imperfectly known. 



New Abyssal Gastropod.§ — MM. Ph. Dautzenberg and H. Fischer 

 describe a remarkable mollusc dredged by the ' Princess Alice ' off the 



* Anat. Anzeig., xvii. (1900) np. 170-2 (2 figs.). Cf. ante, p. 37. 



t Arch. Mikr. Anat., lv. (1900) pp. 300-13 (1 pi.). 



X Zool. Jahrb. (Abt. Anat.), xiii. (1900) pp. 293-35S (4 pis.). 



§ Bull. Soc. Zool. France, xxiv. (1899) pp. 207-11 (4 figs.). 



