326 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
among the wing muscles. In the larva (Plate 1, Figure 3, flz. cox. 
mt’thx. 2) it is composed of three fibres, extending from the dorso-lateral 
portion of the metathorax vertically downward, and attaching to the 
posterior side of the leg. It serves in this stage exclusively as a flexor 
of the coxa, since no wings are present. The three fibres become closely 
approximated during pupal life (Plate 3, Figure 7, jlx. cox. mt’thx. 2). 
The dorsal attachment in the zmago (Plate 5, Figure 11, jlz. cox. mt’ th. 2) 
is to the posterior part of the scutum, from which it extends downward 
and backward to attach to the ventral surface of the middle of the coxa. 
Extensor alae magnus metathoracis of Luks. 
(Extensor antérieur de Vaile of Straus-Dirckheim ; préaxillaire of Amans.) 
The great extensor of the wings is composed in the larva (Plate 1, 
Figure 4, eat. al. mag. mt’thz.) of either three or four fibres, there being 
individual variations. These fibres, which are very short, are found in 
the lateral ventral portion of the metathorax, immediately above the base 
of the larval leg, and extend nearly vertically. They probably have 
some connection with the leg movements. These fibres elongate very 
rapidly in the pupa (Plate 2, Figure 5, ext. al. mag. mt’thz.) and fuse 
completely at their dorsal ends. During this growth, the dorsal end 
shifts its position very noticeably, so that its attachment comes to lie in 
the antero-lateral portion of the somite. By the time the zmaginal state 
(Plate 4, Figure 9, ext. al. mag. mt’thz.) is attained, the muscle has in- 
creased still more in size, and its fibres are so fused as to show but two 
parts, which are separated at the ventral end only. It extends from 
what is known as the large cupule—a tendon formed during pupal 
life — backward and downward to the middle of the lateral expanse of 
the metasternum. The posterior portion of the muscle at its ventral end 
attaches to a chitinous ingrowth from the metasternum. 
This muscle in Colymbetes is also very plainly divided into anterior 
and posterior portions, the division being much plainer than Luks has 
shown for Dytiscus. The division into two parts is not as apparent in 
Synchroa and Bruchus as in Thymalus. 
Extensor alae parvus metathoracis of Luks. 
(Troisiéme fléchisseur de la hanche et extenseur postérieur de Paile of 
Straus-Diirckheim ; postaxillaire of Amans.) 
Besides acting as an extensor of the wing in the imago, this muscle is 
also the third flexor of the metathoracic coxa. It is composed in the larva 
