BREED : METAMORPHOSIS OF THE MUSCLES OF A BEETLE. 335 



At first sight it seems impossible that larval muscles, extending antero- 

 posteriad the full length of the first abdominal somite, should be trans- 

 formed into extensors of the coxa of the imago. In Thymalus, indeed, 

 these muscles have no such function in the imago, but in forms in which 

 the ventral plate of the first abdominal somite becomes completely 

 eliminated, it does not seem improbable that such a shifting of position 

 takes place. In Thymalus their function is that of ventral protractors 

 of the second abdominal somite. 



Extensor coxae metathoracis tertius of Luks. 

 (Troisieme extenseur de la handle of Straus-Dtirckheim.) 



The third extensor of the coxa is present in the larva (Plate 1, Figure 4, 

 ext. cox. mt'thx. 3) as two fibres extending dorso-ventrally from the dorso- 

 lateral part of the metathorax to the ventro-lateral part. In the jnipa 

 (Plate 2, Figure 5, ext. cox. mfthx. 3) the ventral attachment is shifted 

 posteriorly, so that the muscle extends obliquely from an antero-dorsal 

 to a postero-ventral position. The origin of this muscle in the imago 

 (Plate 4, Figure 9, ext. cox. mfthx. 3) is on the lateral edge of the 

 scutum and the insertion, on the dorso-median edge of the coxa. 



Extensor trochanteris metathoracis of Luks. 

 {Extenseur du trochanter of Straus-Dtirckheim.) 



The extensor of the trochanter in the imago is divided into two parts, — 

 the long and the short heads. In the reconstruction only the pupal and 

 imaginal conditions of the long head have been determined. In the pupa 

 a muscle (Plate 3, Figure 7, e.xt. trchn. 7nt'thx.) is found which shows 

 histologically that it is a metamorphosed larval fibre ; this forms the long 

 head of the extensor trochanteris in the imago (Plate 3, Figure 7, ext. 

 trchn. mfthx.). Its origin is on the posterior face of the lateral wing of 

 the metafurca (mffur. <?), very close to the origin of the first extensor of 

 the coxa. Its insertion is on an apodeme which projects from the median 

 side of the trochanter. The short head of this muscle attaches to the 

 same apodeme, and would show in the same figures as the long head, if it 

 had been reconstructed. 



The flexor trochanteris metathoracis would likewise have been visible in 

 Figure 7 (Plate 3) and Figure 11 (Plate 5), if it had been reconstructed. 



The remainder of the imaginal leg muscles are metamorphosed larval 

 muscles. The details of their changes have not been studied out. 



This ends the description of the changes of the lateral dorso-ventral 



