304 THE EFFECT OF FOOD 



the atmosphere he found to be much more important 

 than differences of volume. Thus a snail kept five 

 months in a litre of water having a surface of 18 cm. in 

 diameter attained to nearly twice the length of one 

 kept in an equal volume of water which had a surface 

 of only 2 cm. diameter. In order to test Semper's 

 hypothesis of the essential substance in the water, De 

 Yarigny suspended a glass tube 2 to 3 cm. in diameter 

 in various sized vessels of water. A piece of muslin 

 was tied over the bottom of the tube, so as to permit 

 of interchange of water, but prevent the snails placed 

 in the tube and in the outer vessel of water from inter- 

 migrating. After two to five months' growth it was 

 found that the snail placed in an outer vessel of 4200 

 cc. capacity sometimes attained to more than twice 

 the length of that placed in an inner one of 250 cc. 

 capacity. Again, snails were placed in two tubes of 

 the same size, one of which was suspended in a vessel 

 containing 100 cc. of water, and the other in a vessel 

 containing 1150 cc.; in another similar experiment th,e 

 external volumes of water were respectively 50 and 500 

 cc. In each case, however, the snails in the two inner 

 vessels attained to practically the same size. Still 

 again, two similar tubes, holding 50 to TO cc. of water, 

 were placed in a vessel containing 4200 cc. of water. 

 One tube was closed with muslin, and the other with a 

 tight-fitting cork, which of course prevented all inter- 

 change with the outer vessel of water. Nevertheless 

 the snail in this tube, after two months' growth, was 

 only very slightly smaller than that in the other 

 tube, but both of them were only about three-fifths the 

 size of the shell grown in the external vessel. It should 



