14 BRITISH LEPIDOPTERA. 



adult plumage, suggesting that formerly the adult plumage was 

 attained by a gradual development, and that the present abrupt 

 transition occurs by the suppression of the now lost intermediate 

 stages. A not infrequent form of plumage exhibited in the extra 

 instar is like the present fourth instar with certain adult characters 

 superadded. Chapman notes another form of plumage correlated with 

 the extra skin (only observed in one specimen) more like the adult 

 than the juvenile form, but with some juvenile characteristics. The 

 same observer also remarks (Knt. Record, ii., p. 127) that from his 

 observations it would appear in this (and other) species that " a larva 

 temporarily belated by want of food or other circumstances, may die of 

 atrophy, or may display extra vigour, have an extra moult, and finally 

 be a larger specimen than if the normal course had been pursued." 

 He further notes that, in J. alni, the extra-moulter larvae produce 

 moths of both sexes, and further that the variation is not hereditary, 

 as ova obtained from these extra-moulter s in 1888 did not produce a 

 single example in 1889. Chapman concludes that no detailed remarks 

 that he could make, would "add to the evidence that these two forms of 

 larva, with an extra stadium, afford, viz., that J. alni was once a five- 

 moulter like the other species of the genus, and that intermediate 

 forms between the present fourth and fifth instar plumages, at one 

 time existed, some features of which are preserved by these atavistic 

 variations," and he observes that "it is also interesting to note that 

 in the latter (rarer) form, at any rate, some features of other species 

 of the genus are presented, which are quite absent in normal J. alni." 

 Hyhoma strigosa is usually a four-moulter larva, but Chapman notices, 

 out of a brood of some two dozen larva?, four five-moulter larva?. The 

 five-moulters in the fifth instar do not assume the ordinary adult 

 plumage, the plumage of the extra moult not differing much from that 

 of the fourth instar. 



The same observer has also noted (Ent. Record, iv., pp. 265 ct seq.) 

 in Arctia caza, not only variations in the number of moults, but that 

 variation, both in plumage and habits, may be associated with the 

 variation in moulting. This species normally hybernates in the fifth 

 instar, and moults thrice (sometimes twice and occasionally four times) 

 after hybernation. However many instars the larva may pass, nine, 

 eight, seven, or six, the adult plumage is usually reached only in the 

 last two instars. In every brood a certain percentage (about five per 

 cent.) feed up rapidly in the fourth instar, become larger in this, than 

 is the normal larva in the fifth, instar, and at the fifth moult, these pass 

 into the caia (adult) plumage. These larva? generally become full-grown 

 in the sixth stadium, whilst others do so in the seventh, and emerge as 

 moths in from eleven to thirteen weeks from the date of the eggs being 

 laid, these are called the " Forwards." The great mass of larvae, 

 however, are of the " Normal " type, have eight instars, moulting four 

 times before hybernation and three times after, and produce moths 

 within a few days of twelve months of the eggs being laid. Others 

 progress slowly and get in extra moults (one or two) before obtaining 

 adult plumage. These are called "Laggards." A series of pedigree 

 experiments on " Forwards " and " Normals " (Knt. Record, iv., 

 pp. 288 ct seq.), and "Laggards" (loc. cit., v., pp. 33 etseq.), are detailed, 

 by which it appears that the elimination of a peculiar "Forward" 

 race is dependent on temperature, and that a certain percentage of every 



