46 THE CHRYSALIS. 



in which the prothorax of the larva is immensely 

 enlarged, permitting, as we have seen, the entire 

 withdrawal of the head. 



There is only one other point in connection 

 with the thorax which need detain us. In the 

 caterpillar we found a spiracle in the middle of 

 the side of the first ring. In the chrysalis, how- 

 ever, we have shown that the middle joint of the 

 thorax is developed at the expense of the front 

 joint, and the latter is further curtailed by the 

 sheaths covering the extended mouth-parts to such 

 a degree that it is reduced externally to a slender 

 dorsal plate ; the spiracle is therefore transferred 

 to the suture between the outer portion of this 

 dorsal plate and the middle joint ; indeed it 

 seems rather to belong to the latter, for it is often 

 protected at this point by a thickening of the 

 middle joint, occasionally developing to a tubercle 

 [Fig. 63] ; this spiracle and those 

 upon the sides of the abdominal 

 joints are the only openings into the 

 interior of the body ; the digestive 

 tube is closed at both ends ; no 

 glands find an external outlet, and 



Tityrus, showing 



1 * h ? r J C 2 CSplracleat so l^tle aeration is required for the 

 fluids of the body during its strange 

 dormancy, that in the higher groups this thoracic 

 spiracle is lost and the larger part of the body 

 receives its air through the openings at the op- 



