20 JEFFERY : ON THE HAIRS OF MOLLUSCA, &C. 



Observations made of the lip of snails' shells while in the 

 process of formation have, I believe, revealed to me the fact 

 that the bristles are formed in the first place not in a perpendicu- 

 lar, but in a horizontal, position, i.e., in a line with the continua- 

 tion of the whorl. 



We will suppose, as I think is the generally accepted 

 theory, that the whole thickness of the shell is formed in several 

 layers. If we take a snail with its shell in the process of forma- 

 tion, we find the extreme edge of the mouth very thin and 

 fragile, and we may take it that the epidermis being the outer 

 coating, is the first formed, and with that the epidermal hairs 

 or bristles, which I imagine to be formed in a line with the 

 growth, a fringe as it were on the edge, lying on the surface of 

 the mantle, and of course in the earliest stage in a state of thick 

 mucus, which fringe gradually hardening with the epidermis 

 is by the formation of the under layer next following, which 

 probably includes in most cases some calcareous matter, gradu- 

 ally forced into a perpendicular position, or one nearly approach- 

 ing it, while the points of the fringe, being last formed, are least 

 hardened, thus accounting for the drooping of the points of the 

 bristles. 



Probably other collectors, as well as myself, have noticed 

 that if on coming home from a day's collecting too late, or too 

 tired, to pay proper attention to the molluscs collected, they 

 will be found next day, where huddled together in the box, 

 bottle, or bag, to have made considerable depredations on the 

 shells of each other by gnawing off patches of the epidermis, 

 either in exasperation at the confinement or from hunger, and 

 in such cases those which have bristles are quickly denuded of 

 them. This has happened to me with H. ohvoluta. 



We are here brought to another point illustrating the same 

 process of denudation. As each succeeding whorl of a shell 

 being formed overlaps the preceding the bristles have to be 

 stripped from the periphery, for they would be objectionable on 

 the inner wall of the molluscan home, and this must be the 

 work of the jaw of the mollusc itself. 



J.C., v., January, 1886. 



