248 



HARD WICKE'S SCIENCE- G OS SIP. 



• r>f the animal as well as of the shell. Whether the 

 colouring of the shell has been acquired in a manner 

 similar to that of birds' eggs I am not prepared to 



,give any opinion, but in a paper on the colouring of 

 birds' eggs, published by Lucas, on pp. 52-60 of the 



.twenty-fourth volume of the " Transactions of the 

 Royal Society of Victoria," last year, there are one or 



..two suggestions which are legitimately applicable to 

 the mollusca. Mr. Lucas considers that the effect of 



.-environmental conditions upon the nervous constitu- 

 tion of the bird while the shell is in formation is a 

 very important factor in producing colour-variations 

 in the egg. But that the bird is restricted by tribal 



^.habits of preceding generations, so that, no matter 



■ what colour-variation there is, a good ornithologist 

 Oknows the particular species of bird to which any 



particular egg belongs. By a suitable changing of 

 words, I am of the opinion that his theory equally 

 iipplies to the colour-variations of molluscan shells. 

 It would be interesting to know whether food has 

 any influence on the production of colour-variation 

 -in shells. Miss Hele, I know, has recorded the 

 darkening of the shell of H. aspcrsa by feeding the 

 .animal upon lettuce, a circumstance which I attribute 

 to the absorption of an alkaloid, or alkaloids, from the 

 Jettuce by the animal. This is a matter upon which 

 all conchologists can work and record. There have 

 recently been two papers published in the " Natura- 

 list," by Gain and Kew, on snail and slug food, but 

 ■they are both mere statements of the names of plants 

 .-upon which this snail or that slug has been seen to 

 .feed — very interesting and worthy in their way, but 

 without any mention of the effect of food upon varia- 

 tion, and without any suggestions or explanations as to 

 why this slug or that snail chooses this or that particular 

 , plant as its food. Consequently, they serve but little 

 43urpose in this relation. But, if I may be allowed 

 . and not be considered as too greatly deviating from 

 iiiy present subject, I would like to refer them and 

 those persons interested in the subject upon which 

 tliey have written, to an exceedingly suggestive 

 ^-laper which has been recently published by Stahl, in 



■ the twenty-second volume of "Jenaische Zeitschr. f. 

 Naturvv.," "■ on the protection afforded by plants 

 against snails. Stahl divides his subject up into two 

 divisions. In his first division — substances contained 

 in the cell -sap of plants as protection against snails — 

 lie includes raphides, bitter principles, tannin, calcium 

 bioxalate, and volatile oils, with the oil receptacles 

 •of liverworts. His second class — external morpho- 



. logical protection of plants against snails — includes 

 the formation of mucilage by water-plants, the im- 



, pregnation of the epidermis by siliceous matters, and 



- stiff hairs. 



Reverting again to variation and the recent pub- 

 lished literature on the subject, whether the theory 

 which the Rev. J. T. Gulich has recently promulgated, 



* See also "Bot. Centralbl.," xxxvi. (1S8S) p. 164. 



in the "Journal of the Linnean Society," of "Direct 

 Evolution through Cumulative Segregation," and 

 which he has been led to formulate on account of 

 some divergence of type in some land-shells of the 

 Sandwich Islands which he could not explain by the 

 theoiy of natural selection, will give us any good and 

 true light into the cause of variation, other than what 

 has been already advanced by Darwin, Wallace, 

 Wagner, and Romanes, is open to some doubt. The 

 whole theory enunciated by him is almost inextricably 

 entangled by a mesh of terminology, that I could not 

 do any justice to the reader by giving a resume of 

 it here, and must refer him to its published source. 



On the other hand, it seems exceedingly probable 

 that Prof. Elmer's now publishing book, " Die Entste- 

 htmg der Arten auf Griind von Vererbeti erworbcne 

 Eigenschaften tiack den Gesetzen organischen Wachs- 

 ens. Ein Beitrag znr einheitlichen Auffasmng der 

 Lcbe^velt" of which the first portion only has been 

 seen by me, will help us to a more thorough under- 

 standing of variation. Of course, with this book I am 

 as equally unable as with Mr. Gulich's paper to give 

 in this place la resume, owing to the large amount of 

 matter and argument contained in Prof. Elmer's 

 pages ; but I may give one or two statements which 

 especially struck me as valuable, and with that finish 

 my communication on the subject of variation. 

 These are, that variations due to the conditions of 

 the surroundings may give rise to distinct species 

 without calling in the aid of natural selection at 

 all; that "variations occur throughout in perfectly 

 definite and only in a few directions, and are due 

 to physico-chemical conditions in the interaction 

 between the material composition of the body and 

 external influences ; " that " varieties and species are 

 essentially nothing but groups of forms which have 

 remained at various stages of a progressive develop- 

 ment " — to the remaining of forms at various stages 

 he gives the term genepistasis ; that all variations 

 express themselves simply as growth in definite 

 directions, since "just because the organic modifica- 

 tion depends upon physico-chemical processes, the 

 result, as in the inorganic crystal, is definite." 

 (Cojtcluded.) 



NOTES ON WORCESTERSHIRE BIRDS. 



AN inquiry was recently made in Science- 

 Gossip, asking information relative to the 

 birds of Worcestershire. I beg to forward a few 

 notes made by me during the summer of 1S87 in 

 the immediate neighbourhood of Worcester and the 

 Valley of the Teme, the result, be it understood, of 

 personal, though incomplete, observation. The 

 nomenclature adopted is from Dresser's "Birds of 

 Europe," and I should like to state that my attention 

 has been drawn to the study of bird-life by that 

 pleasant book, "A Year with the Birds," by "an 

 Oxford tutor." 



