AND OF PRODUCTS OF METABOLISM. 287 



variation. Thus Cooke * states that " a deficiency of 

 lime in the composition of the soil of any particular 

 locality produces very marked effects upon the Mol- 

 lusca which inhabit it; they become small and very thin, 

 occasionally almost transparent. The well-known var. 

 tennis of Helix aspersa occurs on downs in the Channel 

 Islands where calcareous material is scarce. For simi- 

 lar reasons, II. arbustorum develops a var. fusca, which 

 is depressed, very thin, and transparent, at Scilly and 

 also at Lunna I., E. Zetland." 



However, in animal development the supply of in- 

 organic salts is almost always more than sufficient for 

 the needs of the organism, and such variations as are 

 produced are due chiefly to the organic constituents of 

 the food. Among invertebrate animals, our knowl- 

 edge of the direct influence of food is almost confined to 

 certain of the Insecta. In the case of bees, it has been 

 known for a very long time that the quality and quan- 

 tity of the food supplied to the larvae determines 

 whether the reproductive organs shall undergo their 

 full development, and produce fertile queens, or remain 

 undeveloped, and so produce non-fertile working fe- 

 males. According to A. von Planta, the diet of the 

 queen larvae contains twice as much fatty material as 

 that of the worker s.f Again, Eimer has pointed out 

 that in the case of the humble bee, the first brood of 

 ova, laid in the spring, get only a scanty supply of nutri- 

 ment, and develop into small females, which are fertile 

 though they can only produce drones. The next brood 



* Vol. iii., " Cambridge Natural History," p. 89. 



f Quoted from Creddes and Thomson's " Evolution of Sex," p. 43, 



