48 Mr Logan on the Habits of Testaceous Mollusca. 



seven degrees from the equator, and fonr miles from the 

 African coast, are three in number, at least only three are of 

 sufficient importance to deserve notice in this place. They 

 lie in the shape of a hoi'se-shoe, forming inside a beautiful 

 harbour. On these islands two species of that beautiful genus 

 of shells named Achatina were found in great plenty : in shape 

 and size they were nearly the same, bvit in colouring very dif- 

 ferent. The full-grown shell was four inches long, and one 

 and a half wide at the mouth : such as seemed to have com- 

 pleted only the fii'st stage of their existence, were not more 

 than one inch in length. The phenomenon that excited my 

 curiosity, and led to the ascertainment of the following facts, 

 was that of finding many of them in a torpid or dormant state. 

 It is known almost to every one, that, in northern latitudes, 

 the Helices, and I believe, all the shelled mollusca of a ter- 

 restrial kind, after having placed themselves, at the approach 

 of winter, under proper shelter, such as old walls, holes in 

 rocks, beneath stones, &c., make an earthy or calcareous oper- 

 culum which exactly fits the mouth of the shell, after which the 

 animal becomes torpid or dormant. This condition is empha- 

 tically called Hybernation. Until the above facts presented 

 themselves to me, I supposed (and every thing that I had read 

 or heard on the subject, tended to confirm the very plausible 

 opinion), that cold was the only cause of torpidity in these 

 animals, and that nature had provided them with a power of 

 forming this crust to protect them from the cold, and the in- 

 trusion of insects or vermes, which might prove fatal to the ani- 

 mal during its state of dormancy. In these latitudes, how- 

 ever, within seven degrees of the equator, they have no winter 

 to provide against, nor cold to produce torpidity ; yet here, as 

 in Europe, they are to be found in an inactive state, and seenf- 

 ingly benumbed, shut up in their shells and covered over with 

 a pure white, firm, calcareous operculum, which is nicely fitted 

 to the mouth of the shell, and fastened with a nuicous or gluey 

 substance. This operculum has no attachment to the animal ; 

 but after a short immersion in warm water, falls oft", leaving 

 the mouth of the shell smooth and entire. 



These observations having established one fact, that cold 

 could not be the cause of torpidity, at least amongst the mol- 



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