bkeed: metamokphosis of the muscles of a beetle. 325 



Musculus lateralis metatharacis anterior of Luks. 

 (Elevateur de I'aile of Straus-Diirckheim ; stei-nali-dorsaux of Amans.) 



In the larva (Plate 1, Figure 3, I. mfthx. a.) this muscle is composed 

 of two fibres, extending vertically downwards from the antero-dorso- 

 lateral portion of the metathorax. to their attachment near the anterior 

 edge of the metathoracic leg. It serves as an extensor of the leg. Even 

 in the young p^pa (Plate 3, Figure 7, I. mfthx. a.), these two fibres 

 become so fused that they cannot be distinguished from each other, ex- 

 cept in cross sections of the muscle. In common with the corresponding 

 attachments of all of the dorso-ventral muscles, the ventral attach- 

 ment of this muscle becomes shifted posteriorly by the very consider- 

 able posterior growth of the ventral portion of the metathorax. The 

 muscle, therefore, changes in its general direction, becoming directed 

 obliquely downward and backward. In the imago (Plate 5, Figure 11, 

 Z. mfthx. a.) this muscle forms the anterior portion of the musculus 

 lateralis metathoracis, which serves for the elevation of the wings. At 

 its dorsal end, it attaches to the anterior lateral part of the scutum. 

 Ventrally, it attaches near the median line of the metasternum ; but, 

 contrary to the condition found by Straus-Diirckheim in Melolontha and 

 by Luks in Dytiscus, no fibres attach to the lateral faces of the median 

 lamina of the metafurca (inffur. 4). 



Musculus lateralis metathoracis posterior of Luks. 

 (Synonymy as with the anterior muscle.) 



This muscle is found in the larva (Plate 1, Figure 3, I. mfthx. p.) 

 as a single fibre immediately posterior to musculus lateralis metathoracis 

 anterior, with which it is nearly parallel. This relation is continued in 

 all stages of the pupa (Plate 3, Figure 7, I. mfthx. p.) and in the 

 imago (Plate 5, Figure 11, I. mfthx. p.). The muscle attaches in 

 the imago, dorsally, to the lateral portion of the scutum and, ventrally, 

 near the median line of the metasternum. In the adult Thymalus, the 

 anterior and posterior muscles are separated farther from each other than 

 in tlie larva ; but in the other beetles examined, as well as in Dytiscus 

 (Luks), they may be so fused that they cannot be readily distinguished 

 from each other. 



Flexor coxae vietathoracis secundus of Luks. 

 (Second flechisseur de la hanche of Straus-Diirckheim.) 



While this muscle acts as a flexor of the posterior coxa, it also acts in 

 the imago as an elevator of the Aving. It is, therefore, described here 



