VARIATION OF EUROPEAN LEPIDOPTERA. 101 



insect to change its normal habits. Hybrids the author denned 

 to be irregular attempts to establish, " per saltum " and in a 

 single generation, what natural law permits only to be effected 

 step by step, — that is, the inauguration of a new species, — and the 

 penalty for such infraction is extinction, and accordingly hybrids 

 are infertile. 



The authority of Boisduval was quoted to show that among 

 such closely related species as some of the Zygsenidte, which 

 frequently are found to couple unnaturally, the ova is invariably 

 infertile. Deformities, monstrosities, and hermaphroditism were 

 then touched upon very cursorily, and the influence of locality 

 and soils were dealt with, the conclusion being that the 

 influences exacted are very small, but may give rise to tendencies, 

 developed subsequently into characters by heredity. Localities 

 isolated from the rest of the world by loft}' mountains, deep 

 forests, or the sea, were pointed out to be thus the most pro- 

 ductive of eccentric forms. Isolation begets peculiarity, and in 

 the remarkable series of Shetland insects taken by Mr. 

 MacArthur we have interesting evidence of the fact. 



The Author summed up as follows : — " Of the past history 

 of species we can only reason from analog}', but on comparison 

 of the forms grouped together in one genus the studen + of classi- 

 fication cannot but be struck with many common points of 

 resemblance which suggest that they are often nearly related to 

 one another, at least ancestrally. But such conclusions must 

 necessarily be merely speculative. We have firmer ground to go 

 upon, however, when we deal with the evolution of species at 

 present in progress. We find that the order of Lepidoptera is 

 subject to many kinds of variation, some attached to one sex 

 only, others depending on the season of emergence ; some which 

 are constant and hereditary, and others which are capricious and 

 irregular in their appearance. Some, too, there are which I have 

 termed ' generic ;' that is to say, that many species of the same 

 genus show a common tendency to vary alike in some particular, 

 and this tendency seems to point to their derivation from a 

 common stock originally. Whatever the exciting causes may be 

 of deviation from the typical pattern, whether climate, soil, 

 quantity, or quality of food, we have seen that the law of heredity 

 is of paramount influence in developing variation so produced, 

 and in transmitting and stereotyping it, as is clearly shown by 



