722 The Zoologist— May, 1867. 



beetles naturally but accidentally associated, as we sometimes find 

 them after a flood, a sarcophage and phytophage, the lion and the 

 lamb, lying down together, and haply a necrophage — like the vulture or 

 the hyaena — curiously examining whether death had yet adapted them 

 to his peculiar taste. 



But in order to render my simile more intelligible, we may imagine 

 Hymenoptei'a and other classes of insects also the victims of the (lood, 

 and that we are busying ourselves in separating and classifying an 

 assembly of which the component parts are incongruous, although 

 associated by Nature herself. In the first place the phenomena of 

 variation offer a convenient division into normal and abnormal. 

 Normal variations are those which must inevitably occur, as from 

 difference of sex, the alternation of generations, or climatal conditions : 

 the first of these has obtained here and there, now and then, a 

 modicum of attention: the second is a perfectly novel field of stud) — 

 a field hitherto uncultivated ; the plough of observation, the harrow of 

 thought, have never touched it: it is still virgin soil; and yet it is 

 certain that a vast proportion, I will not venture to say the majority, 

 of our book species owe their origin to this source: the third 

 has become attractive through the labours of Mr. Darwin and your- 

 self. 



There is also another phase of normal variation, which, whether 

 specific or only trivial, is a problem requiring solution. I purpose 

 recapitulating and extending my observations on this branch of the 

 inquiry, and also citing in e.vtenso the. profound remarks of Professor 

 Westwood, who has evidently given his best attention to — I would say 

 thrown his whole mind into — the subject. I allude to the existence 

 of pairs of insects, as in the instance of Acronycta Psi and A. tridens. 

 This phase of variation, like those resulting from difference of sex or 

 climate, or from alternation of generations, is rendered imperative by 

 some law of Nature hitherto undiscovered. 



Abnormal variation stands on a very different footing, and requires 

 a very different- mode of treatment: it seems in many instances to be 

 a mere freak of Nature, a kind of phrenitis to which she is very 

 subject ; but still there is " a method in her madness," a method that 

 demands our most devoted attention : as examples of this method, I 

 need only mention the frequency of albinism in many quadrupeds and 

 birds, and its utter absence from other quadrupeds and birds, however 

 nearly related : this is but one of the hundred phases that abnormal 

 variation is known to assume. 



