METAMORPHOSIS IN LEPIDOPTERA. 15 



brood has a tendency to develop into " Forwards " under ordinary con- 

 ditions. The experiments show that selection of, and breeding from, 

 "Forwards," does not tend to develop a purely "Forward" race, 

 whereas, a portion of a brood, bred at 80° F., yielded 75 per cent. 

 '• Forwards," the other portion of the same brood bred at 60°-65° F., 

 yielding only 5 per cent., and whilst the latter took three months to 

 complete their cycle of metamorphoses, the former had completed 

 them in two months. These " Forwards," i.e., individuals which 

 feed up, and emerge in autumn are occasionally met with in nature, 

 but must be considered as very rare. Further observations (loc. cit.) 

 showed that much further variation was noticeable, many examples 

 not reaching the hybernating stage (and plumage) until they had 

 moulted five or even six times, i.e., had reached the sixth or seventh 

 instar. These would then after a short hybernation subdivide, one 

 part maturing rapidly and assuming the adult plumage, the other part 

 tending toAvards the "Laggard" type and maturing much more 

 slowly. 



As to the correlation between the rapidity of moulting and the 

 plumage assumed, Chapman writes : — " In all cases the Laggards fed 

 more slowly and made less growth at each moult than the Normals, so 

 that a Laggard would be only in its third instar when a Normal was 

 already prepared to hybernate in its fifth instar ; the former also 

 would, in its fifth instar, be no further advanced as regards size and 

 plumage than a Normal in its third or fourth instar (vide, Ent. Record, 

 v., pi. ii., figs. 1, 2, 8). In one case a Laggard did not reach its last 

 instar until after thirteen moults. Others would pass on to the adult 

 plumage and progress more rapidly after reaching a certain stage 

 . Individuals would begin hybernation at very uncertain stages, 

 some in " Spilosoma " (normal for fourth instar), some in "fidiginosa" 

 (normal for fifth instar), others in "caia" (normal for sixth instar) 

 plumage. It also happened that some aberrant Normals in the later 

 broods prepared to hybernate in distinctly adult "caia" plumage. 

 The following tabulation of the principal and most distinct forms is 

 interesting : — 



Forwards. — 1. Passes from 4th (Spilosoma) to 5th (caia) plumage, omitting 

 fulginosa plumage, feeds up rapidly, and does not hybernate. 



a. Adult in 6th instar. 



b. Adult in 7th instar. 



Normals. — 2. Fidiginosa plumage in 5th instar in which it hybernates ; caia 

 plumage in 6th instar. 



a. Adult in 7th instar. 



b. Adult in 8th instar. 



3. Larger form, with more profound hybernation. 



4. Assumes fidiginosa plumage in 6th instar after hybernation, 



adult in 8th and 9th instars. 



5. Assumes fidiginosa plumage and hybernates in 6th instar. 

 Laggards. — 6. Feeds slowly, never assumes distinct fidiginosa plumage; 



reaches caia plumage in 8th and 9th instars. 

 7. Many variations, in which hybernation takes place in 6th, 7th, 

 8th, or 9th instar, and either in fidiginosa or caia plumage. 



Chapman then notes that he has several times taken Laggards at large, 

 i.e., larv;u apparently in the plumage of the third or fourth instar found 

 in September and October, and that have fed on slowly without going 

 into "fidiginosa" plumage or attempting to hybernate. It is certain, 

 therefore, that though, in England, the great mass of A. ccu'a larvae are 



