The Cowries, Venus Shells 



dissolves its shell when it becomes too tight a fit, and secretes 

 a new one of larger size. 



Reeve quotes a letter from Lieutenant Hankey of the Royal 

 Navy, written in 1844, in which this gentlemen declared that he 

 had seen more than one specimen crawl away into a sheltered 

 hollow, where the shell, enveloped in the mantle lobes, became 

 thinner and dull in colour and finally cracked, by muscular force 

 exerted within. Next the solvent completed its work, leaving 

 a naked mollusk, which soon secreted a transparent, glutinous 

 shell, with a distinct spire and wide lip (the Cymbium shape of 

 all juvenile cowry shells), which rapidly took on thickness, 

 covered the spire, narrowed the aperture, thickened and toothed 

 the two lips and painted the various layers of enamel according 

 to the specific pattern. 



His reasons for not collecting a series of these remarkable 

 shells in process of reconstruction were: ( i ) the extreme rarity 

 of the occurrence described; and ( 2 ) the extreme fragility of the 

 shell in its transparent state. It went into bits as if made of 

 shellac when taken up. 



Reeve politely discredits much of the account, as do subse- 

 quent authorities. However, it is generally accepted that the 

 inside of the shell, down to the lips, is gradually dissolved as 

 the exterior is added to; by this means room is gained for the 

 growing body. The shell is made largely of carbonate of lime, a 

 substance easily soluble by an acid secretion. It is believed that 

 this process is periodic, occuring but two or three times; and 

 that the readjustment is accomplished in retirement and in a 

 very short time. 



Differences in size of adult shells of one species are believed 

 to be individual. The stage of development of a shell may be 

 roughly estimated by the shape, size, colour and pattern. Cy- 

 prcea exanthema is typical. The young mollusk has a thin bulla- 

 shaped shell, with wide aperture, and prominent spire. The 

 surface is banded with flame-like streaks of brown. Gradually 

 the lip thickens on the side next to the aperture, while the back 

 and sides receive layers from the mantle edge which bury the 

 coils of the spire completely. Lip and columella grow closer 

 together and become toothed. Coloured layers alternate with 

 thin coats of white enamel. The final layer of colour is in bright 

 spots and the bands are faintly seen under the pale ground colour. 



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