THE RAW MATERIALS OF EVOLUTION 115 



must be referred to in connection with the origin 

 of variations. It has been shown experimentally 

 that chemical substances in the food of the mother 

 may be carried on into the offspring. Thus, when 

 the dye known as Sudan is mixed with the 

 food of hens, it appears in the yolk of the egg 

 and eventually in the fatty tissue of the chick. 

 Perhaps this sort of thing is commoner than is 

 usually supposed. By changing the temperature 

 and the food of the caterpillars of Vanessa and 

 Arctia, Standfuss and Fischer were able to induce, 

 in the next generation, aberrant characters, which 

 remained distinct when crossed with the parent 

 form. 



More striking, however, are the experiments 

 carried on for twelve years by Professor Tower 

 on beetles of the genus Leptinotarsa, which he 

 subjected to unusual conditions of temperature 

 and moisture when the male or female reproductive 

 organs were at a fixed point in their development. 

 The result was to induce in the offspring striking 

 changes, not only in colour and markings, but 

 also in some details of structure. Sometimes all 

 the germ-cells seemed to be affected, sometimes 

 only a fraction of them ; sometimes various changes 

 resulted from the same treatment ; some of the 

 changes were brusque, others showed intergrades 

 with the parental conditions ; sometimes the 

 change did not occur until after the lapse of 

 several generations in the unusual environment ; 

 there was no reversion to the parental condition. 

 Of course Tower could not get at the reproductive 

 organs except through the body, but it should 

 be noted that the body of the parent was not 

 changed, and it was only at particular stages 



