174 Gaspartl on IIclLv Pomalia. 



Art. XXI. Abstract of a Memoir on the P/ij/siologf/ of 

 Helix Pomalia. By B. Gaspard, M. D.* With Notes 

 br/ T.Bell, Esq. F.L.S. 



[Continued from p. 100.] 



§ 20. Contrary to Swammerdam's representation, these mollusca 

 propagate their species by close contact, raising themselves foot 

 to foot, and remaining in that situation, pressed firmly together, 

 for a whole day or longer ; and at the same time mutually exciting 

 each other with the little dart or needle described by Lister and 

 Duverney. They afterwards retire, partially and gradually, into 

 the shell, from which they do not again emerge until the follow- 

 ing day, when they resume their ordinary habits. After a week 

 or two the act is repeated, and subsequently a third time. 



The little dart mentioned above is formed in the male organs ; 

 I have found it in the vas deferens^ with the point directed forwards. 

 It is a small very white body, brittle, and having a saline appear- 

 ance, of a pyramidal and quadrangular form, or rather having 

 four lateral plates or wings ; it effervesces with acids, and is pro- 

 bably composed of carbonate of lime. I have sometimes found 

 this winged dart, sticking like an arrow, against the genital orifice 

 of the opposite Snail. It exists in the Helix Arbustorum as well 

 as in the present species. 



The interval between the first union and the deposition of the 

 eggs, has varied within my observation, from twenty-five to thirty 

 days. After this period, one only of the two Snails forms a hole 

 in the earth, sheltered from the rain and from drought, and after 

 rounding and enlarging it, introduces the head and neck, and lays 

 the eggs. It then carefully closes and cements the upper part of 

 the nest, and abandons it to the care of nature. 



Two or three days after the eggs are laid, another union takes 

 place, in which that individual which had not laid, is impregnated 

 in its turn, and deposits its eggs three or four weeks afterwards, 



* Mngenclie"s Journ. dc Physiol, loni. ii. p. 295, et. scq. 



