EUTRICHIDS. 119 



to be developed in the other sex, and in its habits (the males 

 flying and assembling at early dusk and later appearing at light to 

 the almost total exclusion of females), approaches the Lachneid (sensu 

 strict.) side of the tree, rather than the other Eutrichids], there is no 

 great range of sexual colour-difference in the remaining more special- 

 ised British Eutrichids. The general tendency in Gastrqpacha tremu- 

 lifolia, G. ilicifolia, G. suberifolia, Dendrolimus pint, and, to a less 

 extent, in Eutricha quercifolia, is to become simply grey in both 

 sexes, a result induced either in response to the conditions of 

 environment, or as a direct outcome of identity of habit in the 

 sexes. As may be expected, however, there is, in these species, 

 a considerable range of variation in the direction of a brighter, 

 or darker, or duller red or red -brown tint, a very common 

 feature throughout the group, and having its origin probably in a 

 phylogenetic basis. Of the numerical relation existing between the 

 sexes in certain Eutrichid species reared by Standfuss, we obtain 

 the following details : 



Odonestis pruni : 1880 — 89 <?s, 81 ? s ; 1882 — 128 S s, 125 ?s=2i7 s s and 

 206 ? s. 



Deitdroliinus fini : 1879 — 782 3 s, 745 ? s. 



Gastropacha ilicifolia : 1882—68 S s, 64 $s; 1892 — 187 $ s, 170 ? s=255 $ s, 

 234 ?»• 



We have already {anted, vol. ii., p. 445) given some notes on 

 the Lachneid antennal structure. Chapman writes : " The general 

 character of the Lachneid antenna is similar to that of many 

 other families ; it closely resembles in many details that of 

 the Lymantriids. It is a pectinate (or plumose) antenna with 

 two plumules to each antennal joint, arising not very far 

 apart on its underside, so that they do not spread laterally, 

 but to some extent hang down side by side below the 

 antenna, lop-eared fashion. In the male antenna these are always 

 well developed ; in the female they are much shorter, but are never 

 quite obsolete. The number of joints appears to be very variable, 

 e.g., in L. querciis from 58 to 78. They are often somewhat oblique, 

 that is, the ventral side is nearer the base than the dorsal. The 

 dorsal area is clothed with scales, the ventral side and plumules have 

 none. In Lagoa, the Cochlidids, and the Arctiids, very similar antennae 

 have the outer surfaces of the plumules clothed with scales. Here, 

 and in the Lymantriids, Dimorphids (Endromids), and in Eriogaster* 

 (Cnethocampa), the plumules bear no scales. The outer aspect has a 

 smooth surface, except that it is covered with very minute spicules, and 

 the inner surface is clothed with regularly-arranged, rather long, hairs. 

 The extremity of the plumule is often a little swollen or clubbed, and 

 carries one or two, usually two, strong bristles, and, in addition, a 

 thick, short, robust spine, that varies a great deal in size, &c, in 

 different species." 



Giinther hints (Bert. Ent. Zeits., liv., pp. 11 — 12) that the 

 differently tinted specimens of Dendrolimus pini may select resting- 

 places that agree with their own particular colour tint. Considering 

 the great variability in the tint of the pine-trunks on which the 

 imagines of this species rest, the explanation that the cause of the 

 variation of this insect is due to natural selection preserving those 



*For the synonymy of the genus Eriogaster (see antea, ii., p. 450). 



