178 THE ENTOMOLOGIST. 



in size southward, and Dr. J. A. Allen has shown that in the eggs 

 of the same species of birds, those in the south are less in 

 number and of smaller size than in the north. Insects, on the 

 other hand, frequently, though not invariably,* increase in size 

 to the southward. These differences appear somewhat anomalous, 

 but remembering that in the Vertebrata an increase of temperature 

 may impair the power of assimilation, while it is not likely to 

 affect insects in this way, at any rate to so great an extent, it 

 is possible to see why size-variation should apparently not follow 

 precisely the same lines in these different classes of animals. 

 Prof. A.S.Packard (Mon. Geom. Moths, ppj^ 588, 589) has shown 

 that, in North America, Lepidoptera increase in size westward, 

 and this he attributes to the warmer and more humid climate of 

 the Pacific slope. Drasteria erechtea, a common North-American 

 moth, appears to reach its maximum size in California and its 

 minimum in the Hudson's Bay Territory (see Fourth Rept. U. S. 

 Ent. Com. 1885, p. 352). A. R. Grote (Can. Ent. xii. 17) 

 mentions examples of Cramhus vidgivagellus and C. topiarias from 

 the west which were smaller than eastern specimens, but the first 

 was from a rather northerly locality (Vancouver Island), and the 

 second from a mountainous district (Sierra Nevada), so they are 

 really only exceptions proving the rule. 



Insects found on small islands are often undersized, and this 

 may easily be due to want of nutriment. Wollaston states that 

 Anthonomus ater, Mshm., averages two lines long, but none of 

 those collected on Lundy Island exceed one line, while 

 CeutJiorhynchus co)itractiis, Mshm., is also small on Lundy. 

 Holme (Trans. Ent. Soc. Lond. ii., pp. 59 — 62) declares that 

 Bolitochara assimilis, Kirby, is invariably smaller in Scilly than 

 near Penzance. But insular faunae are not always dwarfed, even 

 where one would most expect it. St. Kilda " is very bare, being 

 closely fed down with sheep and cattle, and yet," says Mr. C. W. 

 Dale (Entom. xxii. 13), " I can fully endorse Dr. Sharp's 

 remarks of the specimens [of insects] showing no signs of 

 depauperation." It is worth noting, though, that with three 

 exceptions all the St. Kilda Coleoptera are Geodephaga, and such 

 groups as the Chrysomelidse and Curculionidse are (so far as is 

 known) wholly unrepresented. A more curious case is that of 

 the Deserta Grande, one of the Madeira Islands. This island is 

 exceedingly rocky and bare, and I believe closely fed down by 

 riibbits ; yet Wollaston records that several species of beetles, 

 such as Ollsthopus maderensls, WolL, are larger there than on the 

 main island of Madeira. 



* For instance, Vanessa urtlcce is said to be larger in Scotland than in England 

 (F. A. Walker, Entom. xx. 301). 



(To be continued.) 



