CHAPTER VI. 



TRANSFORMATIONS OF THE INTERNAL ORGANS. 



LET ns now look at the changes which the in- 

 ternal parts undergo, as the caterpillar passes 

 through the chrysalis to the imago state. 



To begin with the muscular system, we find the 

 principal differences between the caterpillar and 

 imago to exist in the head and thorax ; in the 

 abdomen the muscles moving the different joints 

 are much the same, although greatly reduced in 

 size ; the interior of the head, however, presents 

 a very different appearance ; instead of being 

 mainly occupied by muscles moving the horny 

 jaws, the space is nearly all given to brain and 

 optic nerve, and what few muscles there are serve 

 simply to move the antennae, the tongue, and the 

 labial palpi, and to open and close the pharyngeal 

 sac ; these have been developed at the expense of 

 the muscles of the mandibles, which, from occu- 

 pying nearly the whole head, have almost abso- 

 lutely disappeared, since the mandibles are now 

 immovably soldered to the frame-work of the 

 head. The thorax is greatly swollen and the 

 longitudinal muscles, instead of merely lining the 



