i9i8. CoLGAN. — Reproduction of the Common Snail. 167 



French investigator, M. P. J. F. Turpin, had forestalled 

 me by eighty-seven years in the discovery of the carbonate 

 of lime crystals in the egg-shell of the garden snail. His 

 paper, illustrated by excellent figures, was read before the 

 French Royal Academy of Sciences in 1831 and published 

 the following year in the Annales des Sciences Naturelles.^ 

 In all points but one, and that not the least interesting, 

 M. Turpin's observations and conclusions agree with 

 those just detailed. This disagreement occurs on page 

 448, where he poses the question whether the crystals in 

 the outer envelope of the egg are designed to serve in the 

 formation of the young snail-shell, a question, which, he 

 tells us, he would have been almost ashamed to ask had it 

 not been addressed to him by several zoologists. He answers 

 with a decided negative, asserting that these crystals are 

 no more destined to form the shell of the young snail than 

 the shell of the bird's egg is destined to form the bird's 

 bones. This opinion he bases partly on analogy and partly 

 on insufficient or erroneous observation ; for he states that 

 the crystals are always found investing the shell of the 

 snail's egg after the animal has been hatched. As has just 

 been shown here, this statement is at variance with fact, 

 in so far, at all events, as Irish eggs are concerned. The 

 gradual disappearance from the outer egg-envelope of the 

 carbonate of lime crystals pari passu with the growth of 

 the shell formed of the same substance in a non-crystalline 

 state, seems to point to the formation of the shell from the 

 crystals by the action of those vital processes of which we 

 have still so much to learn. In spite, then, of M. Turpin's 

 opinion, it is open to us to maintain that a portion of the 

 crystals detached from the outer coating of the egg is dis- 

 solved and utilized as shell material by the still unhatched 

 animal. 



1 Ann, Sci. Nat., vol. xxv., pp. 426-453 — " Analyse microscopique 

 de I'oeuf du Limacon des Jardins {Helix aspersa Linn.) et d s nombreux 

 Cristaux rhomboedres de carbonate de chaux qui se forment a la paroi 

 interieure de I'enveloppe exterieure de cet oeuf, enveloppe qui sert aux 

 cristaux d'une sorte de geode." A committee of eminent chemists, to 

 whom the question was referred by the Academy, reported in favour 

 of M. Turpin's conclusion that the crystals were carbonate of lime. 



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