18 BRITISH LEPIDOPTERA. 



phenomenon is well illustrated by the larvae of many of our common 

 Sphingids and Notodonts. Among the American species, Dyar notes 

 FAideilinea Jiermidata which, normally green, becomes bright red, 

 Heterogenea shurtleffii which loses all its pigment and becomes trans- 

 parent, Polygrammate hebraicum which, normally green, assumes a 

 complicated pattern of lines and spots, &c. This colour-change is 

 undoubtedly useful protectively, but its physiological nature is not at all 

 well understood, although it is no doubt associated with the separation 

 of the larval epidermis and the growth of the pupal cuticle, and may 

 be due to the breaking up of the cells of the former, the change of 

 colour being simply a result of the active physiological processes in 

 progress at this time. 



It has been noted that, when the true legs of certain lepidopterous 

 larva? have become lost by injury, they have been reproduced at 

 successive moults but usually in diminished size. Reaumur, Graber, 

 Newport, Ktinckel and others have experimented on larvae, the 

 first-named stating that, having cut off more than half of the three 

 thoracic legs of a larva on one side, they were, in the pupa, shorter than 

 the three corresponding ones on the other side. Newport also cut off 

 one of the larval legs, and the imago appeared with an atrophied foot. 

 Gonin states that he repeated a similar experiment to that of Reaumur 

 on a somewhat younger caterpillar, and the chrysalis again showed 

 three maimed limbs. He also states that the true leg of the larva 

 corresponds only with the tarsus of the imago, or, in other words, we 

 surmise, contains only the imaginal disc that forms the tarsus of 

 the imago. The removal of the leg of the caterpillar, therefore, only 

 removes that portion of the internal structures that will develop later 

 into the tarsus, the femur and tibia remaining intact. Birchall notes 

 (Ent. Mo. Mag., xiii., p. 232) that a larva of S.fagi that he observed 

 had "lost the whole of one of the second pair of legs except the coxa, 

 also nearly the whole of the caudal horn on the same side . . . 

 at none of the three subsequent changes of skin which took place was 

 there any renewal of the missing members, or increase in the length 

 of the stumps." Experiments of ablation cannot be considered con- 

 clusive on account of the regeneration of parts. To us it appears 

 certain that the correct explanation is — that the imaginal leg buds out 

 of the larval one, and finds a lodgment for some of its elements in the 

 thorax at the base of the leg. 



We have already observed that the final larval ecdysis, by which 

 the pupal stage is assumed, differs but little in its essence from the 

 preceding ecdyses, in fact, the phenomena attending post-embryonic 

 metamorphosis may be really considered as an extension of embryonic 

 life, the change in the external appearance being really but the out- 

 ward manifestations of vital histogenetic changes Avithin, but whilst 

 the histogenetic changes are gradual, the external changes in form are 

 more or less abrupt. Uusually, however, the larva adopts some special 

 means for its protection during this period, and spins a cocoon, makes 

 an underground chamber, or suspends itself in a position where its 

 resemblance to its surroundings will aid in its protection, before 

 changing into the pupal form. Nor is the change to a pupa really so 

 sudden as it appears, for the larva, for some days (variable in number) 

 before its actual change, passes through a quiescent period, in which 

 the pupal organs are more or less perfected, and even before the 



