398 



We must see, then, the importance of getting together in our 

 cabinets in all cases as large a number of varieties as can be obtained. 

 It is by the study of these alone, in connection with the particular 

 circumstances under which they are found living, that we can 

 arrive at any theory of variation, much more approach the question, 

 how species have originated ? * 



Britain is said to be considered by foreign entomologists as rich 

 in varieties ; and Mr. MacLachan, who has paid great attention to 

 the variation of Lepidopterous insects, attributes the circumstance 

 as " due, 1st, to our insular position ; 2ndly, to our anomalous and 

 variable climate, and 3rdly, and perhaps chiefly, to the diversity in 

 the geological structure of these islands." t He doubts, himself, 

 the influence of food in causing variation ; at least he doubts its 

 influence on the imago, though he seems to think it may have some 

 effect upon the larvae or caterpillars, the colours of which often 

 assimilate themselves to those of the plants on which they subsist, 

 being a case of mimicry for protective purposes. Other ento- 

 mologists, however, are of a different opinion on this last point. 

 Professor Westwood has recorded an instance in which there would 

 seem to have been clear evidence of the influence of food upon the 

 perfect insect. A number of caterpillars having been hatched from 

 a particular lot of eggs of the Liparis dispar, or gypsey moth, they 

 were divided into two portions, some being fed on elm, others on 

 whitethorn. There was no difference in the larvae, cocoons, or 

 pupae ; but the male moths fed on elm were larger, and the colours 



* So long back as 1839, Isidore Geofiroy St. Hilaire spoke of the importance 

 of attending to local varieties of animals, and appreciating those slight dif- 

 ferences arising from the influence of local circumstances " tending to 

 establish the passage of one species into another." He considered such 

 inquiries as possibly one day affording a key to the solution of the difficulties 

 which beset the study of zoology, and an answer to " important questions 

 affecting the very philosophy of science." He says, " if it be of importance 

 to zoology to enumerate animal species with exactness, and carefully to note 

 the differences which disting^sh them, are not the origin and formation of 

 species, the nature and causes of their differences, likewise questions of real, 

 nay, of immense interest." This was written twenty years before the publi- 

 cation of Darwin's " Origin of Species." — See Edinb. New Phil. Journ., vol. 

 xxviii., pp. 65 and 65-67. 



t Ent. Trans., 3rd Ser., vol. 2, p. 458. 



