ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 37 



otocyst was represented by a compact evagination, a fact which recalls 

 Herbst's exogastrulae in sea-urchins. It is suggested that the changes 

 in the division processes, e. g. from indirect to direct, are not the direct 

 result of the solutions, but are due to accumulations of certain substances 

 in the cells, i. e. are the expressions of induced cellular degeneration. 



y. Gastropoda. 



"Varieties" of Helix pomatia.* — HerrO. Buchner protests against 

 the careless use of the term " variety." " A true variety," he says, 

 " forms the bridge towards the formation of a new species." A variety 

 cannot be established unless it be shown that there are constantly 

 inherited novel characters iuterpretable as adaptive to particular con- 

 ditions. An individual variation must not be made the basis of a variety, 

 nor a hybrid, nor a monstrosity. 



Varieties whose characters relate to form, structure, and colour of 

 the shell, may be due either to internal germinal changes, or to external 

 environmental conditions, but the latter (varieties due to " modification," 

 sensu stricto) only persist as long as the operative influences persist. 

 That either of these kinds of variety really exists in the case of Helix 

 pomatia seems to Buchner more than doubtful ; so that he finds a pro- 

 visional solution (in his museum arrangement) in naming, besides the 

 normal, four " form-types " — inflata, spheeralis, plagiostoma, and turrita. 

 There are differences in the distribution of these form-types ; but the 

 author will not at present commit himself to any statement as to the 

 causes determining the four main forms which he ranges round the forma 

 vulgaris. 



Intestinal Epithelium of Helix, f — Herr W. Ellermann states that 

 in the snail the structure of the ciliated epithelium is strikingly different 

 from that of Anodonta. He finds that the striped appearance, regarded 

 by Heidenhain as due to the existence of protoplasmic fibres (the roots 

 of the cilia) like those of Anodonta, is in reality produced by a folding 

 of the cell-surface in the long axis. This is clearly seen in transverse 

 sections. The folding the author believes to exist in the living cells, and 

 not to be an artificial product. True cilia roots were found in certain 

 of the cells of the digestive gland, but not in the intestinal cells. This 

 confirms the view that these structures do not invariably occur in 

 ciliated cells. The snails investigated were H. pomatia and H. 

 nemoralis. 



Sensory Cells of Helix. J— Dr. H. Smidt has used Golgi's method for 

 the study of the sensory cells of the mouth-cavity of the snail. He 

 finds that these take three distinct forms. In the lateral lips the cells 

 are prolonged into an excessively fine fibril which terminates in a 

 variously shaped swelling, often of conical form. The presence of this 

 terminal knob was not invariably demonstrated. The two other types 

 occur in the mucous membrane of the pharynx, where a cuticle is present. 

 In the one — the hair-cells — a short thickened fibril ends in a slender 



* Jahreeheft Ver. Naturk. Wiirttemberg, lv. (1899) pp. 232-79 (4 pis.). See 

 Zool. Centralbl., vi. (1899) pp. 873-7. 



t Anat. Anzeig., xvi. (1899) pp. 590-3 (6 figs.). J Tom. cit.,pp. 577-84 (6 figs.). 



