BREED: METAMORPHOSIS OF THE MUSCLES OF A BEETLE. 325 
Musculus lateralis metathoracis anterior of Luks. 
(Hlévateur de Vaile of Straus-Diirckheim ; sternali-dorsaux of Amans.) 
In the larva (Plate 1, Figure 3, J. mé’tha. 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 pupa (Plate 3, Figure 7, l. mt’thx. 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, 
1. mt’thx. 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 (mé’fur. 4). 
Musculus lateralis metathoracts posterior of Luks. 
(Synonymy as with the anterior muscle.) 
This muscle is found in the larva (Plate 1, Figure 3, J. mé’thx. 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, 1. mt’thx. p.) and in the 
imago (Plate 5, Figure 11, l. mé’thx. 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 the 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 metathoracis secundus of Luks. 
(Second fléchisseur de la hanche of Straus-Dirckheim.) 
While this muscle acts as a flexor of the posterior coxa, it also acts in 
the imago as an elevator of the wing. It is, therefore, described here 
