JEFFERY : ON THE HAIRS OF MOLLUSCA, &C. 1 9 



In the case of H. p7ilchella v. costnta, I am setting aside 

 the verdict of the referees of the Conchological Society, under 

 the impression that the specimens I sent them on October i6th, 

 1882 — the same as now exhibited in the micro-shde — were ex- 

 amined under unfavourable circumstances, and are really of 

 that variety. 



If. lamellata would probably also come in with these, but I 

 am not acquainted with it. 



And now with regard to the way in which these bristles 

 are formed erect, or nearly so, on the surface of the shell — the 

 point to which my attention was at first attracted — I think I 

 may say I have a clue. 



Many plants, perhaps we may go so far as to say most 

 plants, have hairs, some of stellate and other forms interesting 

 as microscopic objects, and here the enquiring mind may ask, 

 how are they formed ? and what purpose do they serve ? 



Why are thistles generally spiny ? or why is the nettle 

 supplied with a poisonous spine-like hair ? 



But this is a matter of growth, which may be compared 

 with that of the mollusc rather than of its shell. 



The snail grows according to the amount of food supply 

 and surrounding influences, but the shell of the snail is generally 

 understood to be formed by matter deposited by the mantle as 

 the mollusc requires it, and probably at its own will and per- 

 ception of the necessity. 



The Holly-leaf is spiny, and is said to become more so 

 about the lower parts of the bushes that are browsed by cattle. 

 This appears as a wise provision in nature to prevent the de- 

 struction of the plant by being constantly fed off, until it has 

 got above the browsing line (where the leaves become less fully 

 armed with spines), and would appear also to be reactionary on 

 the browsing. 



But in our moUusca, so far as our land and freshwater 

 species are concerned, we fail, I think, to trace either protection 

 by the bristle or the necessity for it. 



