342 Natural History of Molluscous Atmnah : — 



lime from the cloak, and that then the growth of the shell 

 goes on as usual, as is indicated by the plain intermediate 

 spaces. We may further suppose, that, when the seminal tur- 

 gescence has subsided, the fluids are carried in greater abun- 

 dance to the skin, whence an accumulation of calcareous matter 

 in the margins of the collar, and a consequent varix or rib. 

 We may make such or similar suppositions, but they are idle 

 and improbable; and I mention the hypothesis rather from 

 respect to its able author than frorii any the slightest convic- 

 tion of its truth. It is inconsistent with analogy to believe 

 that the Mollusca are influenced by the sexual passion ere 

 they have attained maturity, yet the hypothesis supposes that 

 some of them feel its power almost from the date of their 

 birth, and afterwards at very short and frequent intervals ; 

 while others, of the same genus even, are swayed by it at dis- 

 tant periods, and only two or three times during the term of 

 their existence. And in what predicament are those which 

 are plain and ribless ? Are we to believe that their life is love 

 unceasing ; or that it ceases only as the animal reaches ma- 

 turity, and is about to finish the aperture of its edifice ? 



A theory of the formation of shells different from that just 

 explained was once maintained by many naturalists, and 

 amongst others by Klein and Bonnet, men of great learning 

 and celebrity. They said, that the full-grown shell was a mere 

 evolution of the fcetal one, from the addition of matter by in- 

 tusception ; and they supported the theory by the observation, 

 that the shell yet unborn has as many whorls as the adult. 

 The observation is contrary to fact * ; and it is now generally 

 admitted that the collar secretes the material of the building. 

 " It is found to contain in its glands or vessels the carbonate 

 of lime in a free state ; so that, when the surface of the collar 

 is touched by any foreign body, at each point of contact a 

 quantity of it is thrown out mixed with a tenacious mucilage. 

 To be still further convinced of the fact," says M. Gaspard, 

 in an interesting essay on the physiology of the Helix poma- 

 tia, " I cut off" the collar of the mantle, and having thrown it 

 into a dilute acid, a quantity of gas was given off*, and the 

 liquid gave the usual white precipitate with the addition of 

 soda. No other structure similarly treated afforded the same 

 results." f Further, if we drill a hole in the shell, the animal 

 fills it up, not by any secretion from the adjacent portion of 

 skin, but by withdrawing the collar as far as may be neces- 



* See the admirable preface to Muller's Historia Vermkim, vol. ii. p. xxi. 

 and xxiv. 



t Zoological Journal, i. 96. 



