28 SUMMARY OF CURRENT RESEARCHES RELATING TO 



probably phylogenetically) younger. The scales of the anterior and 

 posterior wings show an antero-posterior development. The scales on 

 the thorax and anterior wings hint at a supero-inferior direction of 

 development ; the reverse is seen in the abdomen and posterior wings. 

 The females are more variable than the males, with larger scales, more 

 densely granulated, with more ridges. By frost and great heat an 

 inhibition is brought about, the internal pressure is lessened, and the 

 scales are smaller. Cold without frost is followed by smaller and 

 narrower scales, and the differentiation between basal scales and covering 

 scales disappears. This is a return to a more primitive condition. 

 Warmth without great heat is followed by larger scales in consequence 

 of increased metabolism and haemolymph pressure. Conclusions that 

 apply to characters of wings and body apply also to the scales thereof. 



The male and female copulatory organs are fundamentally identical, 

 but specialized in different directions. They hardly vary in Arctia caja 

 or in species which are not split up into geographical races. The only 

 variability is in the bristles and spines, and this does not affect copula- 

 tion. The invariability of the copulatory apparatus helps to fix specific 

 characters. 



The number of pinnae on the antennae is variable. On an average 

 there are 68 for the male, 64 for the female. Increased temperature 

 reduces the number of joints, decreased temperature thickens and streng- 

 thens them. The distribution and number of sensilla? differ in the two 

 sexes. Great heat and probably frost may inhibit the full development 

 of the sense organs. Moderately decreased temperature induces coarser 

 more massive forms (perhaps more primitive). Moderate warmth 

 favours increase in the number of sensory structures. Frost and great 

 heat are unfavourable to the formation of chitin, but moderate raising 

 and lowering of the temperature are favourable. 



There are correlations between size and sex, between the coloration 

 of the thorax and that of the anterior wings, between the coloration of 

 abdomen and that of the posterior wings, and between the venation and 

 the marking, but no other correlations could be established. 



In the pupa of one day all the parts except the wings show their 

 general structure. The development of hairs, setae, spines, and the like 

 is very slow till about the nineteenth day. The first dress of the Arctia 

 caja as regards wing-form, coloration, setse, scales, etc., is also phylo- 

 genetically the most primitive. The posterior wings show this most 

 clearly. 



The range of colour variation in Arctia caja is enormous, some 

 tending to be lighter, some to be darker. The males tend to one pole, 

 the females to the other. The species is " hyper-sensitive " to influences 

 during the pro-imaginal period. Selection works only on the general 

 aspect, the anterior wings being protective and the posterior wings 

 repellent. There is no evidence of orthogenesis in Eimer's sense. 



Mimicry in Genus Limenitis.* — James Francis Abbott discusses 

 the well known mimicry between Limenitis archippus (a butterfly 

 universally distributed in America) and Anosia (Danaida) plexippus, 



* Washington Univ. Studies, i. (1914) pp. 203-21 (1 pi. and 2 figs.). 



