AND OF SALINITY. 277 



lived in very salt water had become like each other in 

 possessing the characters of thinness, high colour, 

 small beaks, ribbing on the inside, and great relative 

 length. " In view of these four instances of similar 

 variations occurring under similar conditions," says 

 Bateson, " it seems almost certain that these condi- 

 tions are in some way the cause of the variations." In 

 that the variations in the quality, texture, and colour of 

 the shell are found developed to nearly the same degree 

 in all the individuals of successive terraces, Bateson 

 considers they may be fairly supposed to Fe the direct 

 result of environmental change; but the quality of in- 

 creased proportional length is not found in all the in- 

 dividuals, and hence may have arisen in some other 

 way, as by Natural Selection of the type best fitted to 

 live in the altered state. 



A further proof of Bateson's view is afforded by the 

 fact that when the salinity was altered in the direction 

 of diminution, the characters ,of the shells were similarly 

 changed in a reverse direction. Thus, as already men- 

 tioned, the cockles from the very saline lake of Abu Kir 

 resembled those from the lakes of the Aral Sea, but 

 close to this lake are three small areas of water, the 

 Ramleh lakes, of which the water is now quite fresh 

 (owing to their receiving waste water from the irriga- 

 tions). One of these lakes contains living cockles, and 

 another the shells of extinct ones. Now in both in- 

 stances the shells are thick and coarse in texture, and 

 comparatively light-coloured. However, the feature 

 of great proportional length still remains. 



Other evidence as to the relation between salinity 

 and structure in molluscs has been obtained by Gib- 



