JOURNAI, OF CONCHOI.OGY. 209 



copulation is wanting. In Vaginula a channel joins directly 

 the vas deferens with the receptaculum, etc. Therefore^ the 

 possibility of internal self-fertilization cannot be denied, but I think 

 it is likely to be restricted to the cases where peculiar arrange- 

 ments are present for that purpose. We have now enough ex- 

 perience that eggs which commonly are impregnated possess 

 the capability of development without fertilization. In the eggs 

 of Bombyx mo ri the fertilization can be substituted by mechani- 

 cal or chemical irritation, brushing, acids, etc. Most important 

 seems to me the fact that there is a slug in which often the 

 male parts, vas deferens and penis_. are wanting altogether. I have 

 had series of purely female individuals oi Agrioliiiiax Icevis, our 

 smallest cosmopolitan Limacid, from Germany, Madagascar, 

 and Mexico. The figure given by Dr. Scharff- means the 

 same. With this form parthenogenesis is very probable, and 

 therefore, I think, with Avion aier. Mr. Wotton alone is likely 

 to be ableto decide the problem by experiment. For this purpose 

 another individual should be bred under isolation and should be 

 killed after having deposited only a few eggs, the capability 

 of development of which is to be proved. If then no sperma- 

 tozoa are present, either in the receptaculum nor in the 

 genital tube, then parthenogenesis would be demonstrated ; in 

 the contrary case internal self-fertilization would be probable. 

 Certainly the decision would be of high interest. 



Finally, another remark. The restless external parasite 

 Mr. Wolton describes is Acarns limacum, an acarine animal. 



Planorbis aibus v. sulcata. — Shell with strong curved 

 ridges in the line of growth, of which there are about thirty on 

 the last whorl, the intervening spaces being occupied by broad 

 sulci from which the variety takes its name. 



Pond near Leeds. 



To Mr. Nelson belongs the credit of discovering this striking 

 modification of our well-known species. The specimen he kindly 

 presented me with is about the usual size attained by the species 

 in this district, and the usual spiral striation is fairly visible. The 

 upper aspect recalls the general appearance of P. nautileus v. 

 crista minus the spinules. — J. W. Taylor, June 20th, 1893. 



2 R.F.ScharfiF,' The Slugs of Ireland,' Sclent. Trans. R. Dublin Soc, 1891, pi. IviL.fig. 29. 



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