ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 37 



arises as an evagination of the ectodermal fore-gut. The radula fold is 

 developed at an early stage, but the organ itself does not appear till later. 

 It begins with the formation of a cuticular plate by the basal epithelial 

 cells. At the base of the sac, and exactly in the middle line, this plate 

 is elevated, owing to the formation of fresh substance by the odontoblasts, 

 which are the epithelial cells in the fundus of the sac. The further 

 development takes place by the constant formation of new teeth by fresh 

 odontoblasts, which move forward with the teeth, and become converted 

 anteriorly into flattened epithelial cells. Each tooth arises as a thin 

 lamella, continuous in front and at both sides with the cuticular plate ; 

 this forms the back of the tooth, and the body and base are produced by 

 the activity of the odontoblasts. The median row of teeth is the first to 

 be developed, and is followed by two side-rows, and so on in ihis order. 

 The forward move of the embryonic tongue is due only to the gradual 

 growth of odontoblasts and teeth in the forward direction, no motor 

 apparatus being as yet present. 



y. Gastropoda. 

 Experiments on Littorina.* — Prof. K. Mitsukuri has made a number 

 of interesting observations and experiments on Littorina exigna, and 

 formulates the following conclusions: — (1) The mollusc shows a strong 

 negative phototaxis under ordinary circumstances. That this is not due 

 to negative hydrotaxis is shown. (2) There is a disinclination to be 

 submerged, and a rise of water drives the molluscs upwards. When 

 negative phototaxis and negative hydrotaxis act together, the mollusc is 

 driven upward without hesitation ; when they act against each other, at 

 least in small depths, negative phototaxis seems to overcome negative 

 hydrotaxis. (3) In nature they occur scattered over the rocks, because 

 the unevennesses which provide them with holes occur irregularly. On 

 smooth glass plates they move until stopped by some obstacle which 

 they cannot overcome. (4) When splashed on by water for some length 

 of time, as by waves in rising tide, or artificially by a jet, and then left 

 quiet, they may become positively phototactic, and then they go down 

 from the land towards the sea. But they still hesitate on touching the 

 water's edge, which shows that the behaviour is not due to hydrotaxis. 

 {5) While disliking deep water, they cannot live on dry surfaces. They 

 must have a certain amount of water if they are to crawl and feed (?). 

 Those left dry at the highest tide-level pass into a dormant state till the 

 next spring-tide comes round again in a fortnight. (6) The individuals 

 do not seem to wander much. One that was marked had not stirred 

 from the identical spot after an interval of about four months. These 

 remarks probably hold true of L. sitchana var. brevicula, which was also 

 observed, and of other species. It seems likely that the facts under (2) 

 and (5) are the primary ones ; that the animals live by preference on 

 slightly moist surfaces of rocks. " The mollusc probably knows in- 

 stinctively only to go toward dark when water begins to splash it, and 

 to move toward light when splashing has stopped." 



Affinities of Genus Neobeliscus.t— Dr. H. A. Pilsbry modifies some 

 of his former J statements in regard to this genus of South American 



* Annot. Zool. Japon., iv. pp. 1-19 (6 fi£3.). 

 t Proc. Acad. Nat. Sci. Philadelphia, 1901, p. 142. J Op. cit., 1899, p. 36G. 



