326 bulletin: museum of comparative zoology. 



among tlie wing muscles. In the larva (Plate 1, Figure 3, fix. cox. 

 niftJix. 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 impal life (Plate 3, Figure 7, fix. cox. mftlix. 2). 

 The dorsal attachment in the imago (Plate 5, Figure 11, fix. cox. mt'fhx. 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 metathoracu of Luks. 

 {Extensor anterieur de Vaile of Straus-Dilrckheim ; preaxillaire of Anians.) 



The great extensor of the wings is composed in the larva (Plate 1, 

 Figure 4, ext. al. mag. mt'thx.) 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'thx.) 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 imaginal state 

 (Plate 4, Figure 9, ext. al. mag. mftlix.) 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. Tlie posterior portion of the muscle at its ventral end 

 attaches to a chitiuous 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. 

 (Troisieme fiechisseur de la handle et extenseur posterieur de Vaile of 

 Straus-Diirckheim ; postaxillaire of Amans.) 



Besides acting as an extensor of the wing in the imago, this muscle is 

 also the third fiexor of the metathoracic coxa. It is composed in the la^'va 



