260 TORPIDITY. 



clams of three thousand years old precisely resemble the 

 same species which now inhabit the fresh waters of that 

 district ; therefore, the lives of these animals have been 

 greatly prolonged by their exclusion from air and light for 

 more than three thousand years." * 



With the exception of the last example, the others refer 

 to land testacea ; but some pulmoniferous aquatic species 

 are equally capable of assuming this state of torpidity, 

 when under circumstances which deprive them of their re- 

 spiratory medium. In early spring, I have more than once 

 observed the Limnaeus fossarius to abound in small pools 

 of water, which were dried up as the season advanced ; and 

 when, after a careful search, the little snails were found, in 

 a torpid condition, concealed in the cracks made by the 

 drought, or under small clods of earth, where they awaited 

 a happier season to refill their pools, and permit them to 

 resume the functions of active life. Perhaps, in this coun- 

 try, their torpidity can rarely be continued beyond a few 

 weeks ; but in tropical climes similar species can pass the 

 dry season of five long months in this state. Thus, Adan- 

 son informs us that the minute freshwater shell, which he 

 calls Bulimus, is to be seen only from the month of Sep- 

 tember to January, in the marshes of Senegal, formed by 

 the rains which fall in June, July, August, and September. 

 When these marshes are dried up, and, as it were, roasted 

 by the sun, the shell-fish disappear ; a few empty shells 

 alone being left to show where they had been ; but they 

 never fail to return with the rainy season ; and Adanson 

 remarked that, the hotter the preceding summer, the more 

 abundant was the issue of the succeeding hordes. How, 

 asks the author, shall we explain this marvellous reproduc- 

 tion ? Can the eggs of the animal, necessarily very delicate 

 and minute — can they remain in a soil so burned up with- 

 out being entirely dried ; or can the animals themselves, 

 if it is true that they conceal themselves in the bosom of 

 the earth, can they resist during five or six months the heat 

 of a burning sun ? -j- The latter supposition is the only one 

 which can, I think, solve the question. 



When in this torpid state the condition of the snail it- 

 self has not been ascertained. Some authors speak of it 

 as being dormant ; and the language would seem to imply 

 that they consider it in a state of sleep, in which the cir- 

 culation and respiration go on uninterruptedly and as strongly 

 as when awake ; but I suspect that the authors alluded to 



* Silliman's Amer. Journal, No. xv p. 249, as quoted in Turner's 

 Scacred History, p. 473. t Hist. Nat. du Senegal, p. 7. 



