328 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
mt’the. ?) 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. 
(Fléchisseur de Vaile of Straus-Diirckheim ; entopleuro-dorsal of Amans.) 
Larva (Plate 1, Figure 4, flw. al. mt’thx. 1, 2). These flexors are 
found in the larva as single fibres, rnnning 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 pupa 
(Plate 2, Figure 5, flx.al. mt’thx. 1, 2) are changed but slightly. In 
the imago (Plate 4, Figure 9, jlx. al. mt’tha. 1, 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, jlx. al. mt’thx. 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, flz. al. mt’tha. 3 (Plate 2). From 
this mass of tissue is developed the third flexor of the wing in the 
imago (Plate 4, Figure 9, flz. al. mt’thx. 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-Diirck- 
heim for Melolontha that their homologies are somewhat uncertain. The 
third flexor in Thymalus is probably homologous with the three flexors 
ra 
