352 THE ZOOLOGIST. 



being formed as a widely separated pair, were caused to approach the 

 median line, and in about fifty per cent, of the embryos experimented 

 upon the changes were so profound as to give rise to Cyclopean 

 monsters. Many other instances might be cited of definite effects of 

 physical and chemical agencies on particular organs, and we are now 

 forced to admit that inherited tendencies may be completely over- 

 come by a minimal change in the environment. The nature of the 

 organism, therefore, is not all-important, since it yields readily to 

 influences which at one time we should have thought inadequate to 

 produce perceptible changes in it. 



It is open to anyone to argue that, interesting as experiments of 

 this kind may be, they throw no light on the origin of permanent — 

 that is to say, inheritable — modifications of structure. It has for a 

 long time been a matter of common knowledge that individual plants 

 and animals react to their environment, but the modifications induced 

 by these reactions are somatic ; the germ-plasm is not affected, 

 therefore the changes are not inherited, and no permanent effect is 

 produced in the characters of the race or species. It is true that no 

 evidence has yet been produced to show that form-changes as pro- 

 found as those that I have mentioned are transmitted to the offspring. 

 So far the experimenters have not been able to rear the modified 

 organisms beyond the larval stages, and so there are no offspring 

 to show whether cyclopean eyes or modified forms of spicules are in- 

 herited or not. Indeed, it is possible that the balance of organisation 

 of animals thus modified has been upset to such an extent that they 

 are incapable of growing into adults and reproducing their kind. 



But evidence is beginning to accumulate which shows that external 

 conditions may produce changes in the germ-cells as well as in the 

 soma, and that such changes may be specific and of the same kind as 

 similarly produced somatic changes. Further, there is evidence that 

 such germinal changes are inherited — and, indeed, we should expect 

 them to be, because they are germinal. 



The evidence on this subject is as yet meagre, but it is of good 

 quality and comes from more than one source. 



There are the well-known experiments of Weismann, Standfuss, 

 Merrifield, and E. Fischer on the modification of the colour patterns 

 on the wings of various Lepidoptera. 



In the more northern forms of the fire-butterfly, Chrysophanus 

 {PolijommaUis) yhlcBas, the upper surfaces of the wings are of a 

 bright red-gold or copper colour with a narrow black margin, but in 

 Southern Europe the black tends to extend over the whole surface of 

 the wing, and may nearly obliterate the red-gold colour. By exposing 

 pupae of caterpillars collected at Naples to a temperature of 10° C. 

 Weismann obtained butterfles more golden than the Neapolitan, but 

 blacker than the ordinary German race, and conversely, by exposing 

 pupaa of the German variety to a temperature of about 38° C, butter- 

 flies were obtained blacker than the German, but not so black as the 

 Neapolitan variety. Similar deviations from the normal standard 

 have been obtained by like means in various species of Vanessa by 

 Standfuss and Merrifield. Standfuss, working with the small tortoise- 

 shell butterfly {Vanessa urticce), produced colour aberrations by sub- 



