16 



and ' Intelligencer,' and by M. Fologne in the ' Transactions de la Sociele Entorao- 

 logique Beige.' Take again Neptieula uhnivora, which is extremely similar to 

 N. marginecolella, and both larvae mine at the same time in elra leaves, sometimes 

 sharing the same leaf, yet the larvse differ in colour, and mine in a distinct method, 

 and each larva invariably produces an imago having small though constant distinctive 

 characters, so that no one can believe them identical. 



" Similar instances might be multiplied among the Micro-Lepidoptera almost ad 

 injinitxim. Yet it is constantly hinted that two insects, which— in addition to having 

 equal peculiarities with those before meutioned — feed in a different plant, may be only 

 varieties of one caused by the latter circumstance. Now, on the contrary, does it not 

 seem more natural to suppose that, if there were doubt about the matter, this should 

 rather turn the scales, and cause us at once to consider them distinct ? In many 

 genera in which the individual species vary the least the larva of each species affects 

 many different plants, the specimens bred differing only slightly in size and depth of 

 colour. And, again, as far as my small experience goes, the species of other genera 

 have each their own food-plant, or perhaps frequent one or two closely allied species. 

 That differences so great as even to be called varieties can be produced by change of 

 food I must believe to be impossible. All who have paid any attention to breeding 

 Lepidoplera will readily say how impossible it is to produce varieties at will, and how 

 an occasional specimen will make its appearance with such peculiarities of form and 

 markings that, had it been taken at large, with no knowledge of its previous history, it 

 would have stood a fair chauce of remaining undetermined or described as new, but 

 which has been bred from the same brood of eggs kept under precisely the same cir- 

 cumstances. And certain species of Peronea are familiar instances of the imago varying 

 to such an extent that scarcely two can be found precisely alike, while the larvse feed 

 on the same plant and present no differences. On the other hand, in certain genera, 

 for instance Eupilhecia, in many species the larvre, though reared from the same brood 

 of eggs and fed together on the same plant, will vary as much as the imago of Peronea, 

 yet the perfect insects produced from these are identical in appearance. From these 

 and a thousand other instances that might be cited, it does appear to me that variation 

 caused by the food of the larva does not exist, except as to size and tone of coloration, 

 and that any differences in the the number, position and direction of fasciae or spots, 

 iu which consist the distinctive characters of most of the Micro-Lepidoptera in question, 

 can be caused by this means is, as said before, open to the gravest doubts. That such 

 variation can be caused in one or two generations seems to be quite impossible ; and, 

 supposing that any influence can be exercised in this way, it could only be in the 

 course of ages, which theory, however ingenious, and perhaps truthful, it may be, is 

 unfortunately from its very nature incapable of proof.'' 



Professor Westwood observed, with reference to the views advanced by Mr. 

 McLachlan, in the paper just read, that he had endeavoured to guard himself from 

 misapprehension iu speaking of the modification of species produced by change of food. 

 He had indeed given it as his opinion that such a change was capable of occurrence 

 in certain species, although he was in no position to attest it as a fact. In stating that 

 it was difficult to meet this argument, owing to the minuteness of the Micro-Lepidop- 

 tera, Mr. McLachlan had overlooked the fact of the great variation occurring in the 

 largest species of Papilio, as well as Mr. Bates' statement of the variation of the Ama- 

 zonian butterflies, produced, as had been supposed, by a comparatively small geogra- 

 phical range, but which Mr. Westwood was inclined to attribute to other causes, seeing 



