AUG 13 190D ^ 



JOURNAL OF VARIATION. 



Vol. XII. No. 6. June 1st, 1900. 



The Relationship between the Larval and Imaginal Legs of 

 Lepidoptera {u-ith Plate). 



By T. A. CHAPMAN, M.D., F.Z.S., F.E.S. 



The Orthoptera, which we may assume, for our present purpose, to 

 have been the primitive insects, leave the egg with their legs, as far as 

 number of articulations is concerned, except perchance as to tarsal 

 joints, precisely of the same structure as they present in the mature 

 insect. In Lepidoptera this is not so, the larvfe have legs consisting 

 of a basal piece, of three chitinous joints, and a terminal claw, with 

 palpal appendages ; whilst the imago has eight articvilated pieces in 

 the leg besides the claws and appendages. It even happens in some 

 species that the larvje are without legs. This is a common condition 

 in Coleoptera, Diptera, and Hymenoptera. 



On examining the leg-structure of a typical imago of almost any 

 order, we find the tarsus consisting of various articulated segments up 

 to five, of the two long segments, the femur and tibia, and of two basal 

 segments, the coxa and trochanter. If we take a Micropteryx or Erio- 

 crania we find precisely these structures, but if we select any of the 

 higher lepidoptera, say Porthetria dispar, we find this structure present 

 only in the prothoracic legs. In the others the first or coxal piece is 

 soldered to the thorax, and though we may think we see its outlines, 

 it is doubtful whether that is so, so that the statement with which I 

 began, that there are eight articulated segments to the limb, is correct 

 as to these, but the prothoracic leg has nine. 



It is to be remarked here that the larvae of Trichoptera have both 

 coxa and trochanter well-developed, contrasting strongly with their 

 absence in lepidopterous larvae, and making one of the strongest points 

 in their claim to be a separate order from Lepidoptera. Nevertheless 

 the remaining three joints in the larval trichopterous leg, are remark- 

 ably like the three joints in the lepidopterous larva, and since in the 

 trichopterous larva these are unquestionably the femur and tibia and 

 the tarsus reduced to one joint, the close alliance of the two groups 

 justifies us in making the three joints of the larval leg in Lepidoptera 

 the femur, tibia, and tarsus. 



Assuming the descent of the Lepidoptera from some Neuropteron, 

 and ultimately from some Orthopteron with fully developed larval 

 appendages, we are given two theories of how the lepidopterous larva 

 became so worm-like and with such degenerate appendages. One, 

 which I fancy is now obsolete, is that the lepidopterous larva repre- 



