204 THE BIOLOGY OF THE SEASONS 



disturbed, artificial parthenogenesis can be induced in 

 starfish and sea-urchin, in worm and mollusc. Sometimes 

 the result of a slight chemical change is very perplexing, 

 and there are many experiments at which we look with 

 bated breath. Quaint abnormal larvae of sea-urchin and 

 frog are obtained by adding a little lithium salt to the water, 

 and the addition of a pinch of magnesium salt to the sea- 

 water containing embryos of the fish Fundulus heteroclitus 

 induces in a large number of these the development of a 

 single Cyclopean eye in place of the normal two eyes. 

 A small Crustacean called Gammarus, very common in 

 fresh water, has the habit of avoiding the light, but add a 

 little acid so that the solution is no stronger than ^g^th of 

 i per cent., and Gammarus swims towards the light. 

 Remove one or two of the metals from sea- water, keeping 

 up the alkalinity, and the sea-urchin's eggs all develop into 

 twins/' 



The changes that may be brought about by altering 

 the qualities and quantity of the food are so numerous 

 and important, that we cannot wonder at Claude Bernard's 

 saying that evolution was throughout a function of nutri- 

 tion, or at the prominence which some sociologists give to 

 diet as a factor in human evolution. Although Mole- 

 schott's aphorism, " Der Mensch ist was er isst, " seems to 

 over-shoot the mark, the nutritive factor is one of the 

 strongest. Here again we must distinguish between a 

 directly modifying effect and the liberation of a latent 

 character. When we change the colour of canaries and 

 parrots by changing their diet, that seems to be a direct 

 effect ; but it is probable that the abundant and rich food 

 given to the queen-grubs in the beehive is not more than 

 liberating stimulus. Marchal reports that a scale-insect 

 (Lecanium corni) becomes another species (Lecanium 

 robiniantm) when reared on Robinia pseudoacacia instead 



