STRUCTURES IMPLICATED IN METAMORPHOSIS. 1/ 



second and third rings support the wings. The presence of legs 

 and wings involves a considerable development of the segments 

 of the thorax, and particularly of the second and third, for there 

 must be abundance of space within for the passage and attachment 

 of the muscles, which, influenced by the will of the insect, move 

 the legs and the organs of flight. 



The description of the parts of the thorax is not difficult to 

 understand. 



The first segment of the thorax which articulates with the 

 back of the head is called the prothorax ; the second, to which 

 the first pair of wings is attached, is the mesothorax ; and the 

 third, bearing the second pair of wings, is the metathorax. The 

 method of the formation of the abdominal segments is the key 

 to that of those of the thorax. The great development of the 

 mesothorax and metathorax does not usually take place until 

 chrysalis life has progressed. 



The larva of the Calosoina has its thorax well armoured. 

 Above, the three segments are clothed — as is the case with the 

 abdominal rings — with a double dorsal plate with the small lateral 

 piece on either side. This is the upper arch. The dorsal plate 

 is very large, but it does not exhibit any cross markings or 

 any transverse division, but in the adult beetle four distinct parts 

 are added to the two segments that support the wings. The 

 rings of the under part of the thorax of the same larva are prin- 

 cipally membranous. A small plate which is to be observed in 

 the centre of each is the sternal piece. It is very small and 

 rudimentary, but it becomes very large and fully developed in 

 the beetle. 



The mesothorax and metathorax become very large in pro- 

 portion to the rest of the body in the insects which have wings, 

 and are often so united by growth that they cannot be separated. 

 The mesothorax, which supports the first pair of wings, is almost 

 always better developed than the metathorax, and the constituent 

 parts of the first ring are generally more distinguishable than 

 in the last. 



The dorsal piece, so simple in the larva, has four transverse 

 divisions in the beetle, marked out either by ridges or grooves. 

 They can be readily distinguished in the Calosoma sycophanta. 



C 



