328 bulletin: museum of comparative zoology. 



mt'thx. ?) gives rise to the relaxator alae metathoracis. If this "be so, 

 then the two muscles probably remain distinct throughout pupal life. 

 Certainly the positions of these larval fibres correspond very closely -with 

 the positions of the two muscles in the imago, and the identification 

 .seems the more probable when one takes into account the shifting in 

 positions of the extensor alae magnus metathoracis and other muscles 

 which attach near by. There is no doubt but that both of the muscles 

 under discussion are metamorphosed larval muscles, not muscles newly 

 formed in the pupa. 



Flexor alae metathoracis primus et secundus. 

 (^Flechisseur de Vaile of Straus-Dlirckheim ; entopleuro-dorsal of Amans.) 



Larva (Plate 1, Figure 4, fix. al. jnfthx. 1, 2). These flexors are 

 found in the larva as single fibres, running nearly parallel with each 

 other. They extend almost vertically from the dorso-lateral portion 

 of the somite to the ventro-lateral portion. The positions in the pw/>a 

 (Plate 2, Figure 5, fix. al. mfthx. 1, 2) are changed but slightly. In 

 the imago (Plate 4, Figure 9, fix. al. mfthx. l, 2), they extend from the 

 posterior portion of the base of the wing, ventrally and posteriorly, to 

 attach to the dorsal edge of the episternum. 



Flexor alae metathoracis tertius. 

 (Synonymy as in primus and secundus.) 



The facts concerning this muscle are much the same as those con- 

 cerning the relaxator extensoris alae and the relaxator alae metathoracis. 

 In the larva (Plate 1, Figure 3, fix. al. mVthx. 3 ?) there are usually 

 three fibres, sometimes two as shown in the figure. These fibres lie 

 parallel and close together, extending from the antero-lateral portion 

 of the metathorax to the antero-ventro-lateral portion, and show all the 

 evidences of metamorphosis in older larva. In the young pupa it is very 

 difficult to trace their development, but it is probable that they form 

 the mass of tissue shown in Figure 5, fix. al. mfthx. 3 (Plate 2). From 

 this mass of tissue is developed the third flexor of the wing in the 

 imago (Plate 4, Figure 9, fi.c. al. mfthx. 3). This muscle in its adult 

 condition is composed of three parts, which attach by a common tendon 

 on the anterior part of the base of the wing. 



These flexors are so different from those described by Straus-Dilrck- 

 heim for Melolontha that their homologies are somewhat uncertain. The 

 third flexor in Thymalus is probably homologous with the three flexors 



