32 THE BUTTERFLIES OF NEW ENGLAND. 



threads, which collect in a longitudinally disposed mass on each side of and 

 touching- the oesophagus, forming by their couAolutions a fusiform mass 

 which extends to the middle of the metathorax. 



The malpighian vessels arise at the hinder extremity of the stomach, 

 sometimes without the intervention of any basal sac, the three branches 

 arising almost together at a very short distance from the base of their 

 common stem and parting from it at right angles. One of the branches 

 extends along the superior lateral walls of the stomach, as far as the middle 

 of its anterior half (perhaps farther, later in life) and then returns ; the 

 other branch of the outer set passes along the inferior lateral walls of the 

 stomacli ; they are all very delicate, and after their return are strongly con- 

 voluted, enwrapping the intestine but not the colon. 



Respiratory system. The tracheae seem to be nnich as in the larva, 

 only greatly reduced in size, very delicate and not at all opaque. The 

 tubes in the posterior part of the body are small, but from the third abdomi- 

 nal scijment forward they begin to enlarge ; this is especially noticeable in 

 the longitudinal canals, which are everywhere larger than the other vessels, 

 and largest in the first abdominal segments, but again reduced in size in 

 the thorax, where they are less than half their former diameter. 



Circulatory system. The dorsal vessel is a slender, equal canal, lying 

 next the integument of the future imago (86:17). Between the fourth and 

 sixth abdominal segments (behind which it is very obscure) it is firmly 

 attached above, and again in the middle of the thorax, but elsewhere is 

 free; on all the abdominal segments, behind the first, it expands laterally 

 at the posterior limits of the segment ; on the first segment it broadens 

 sliiihtlv, and in front of the expansion begins to diminish gradually and 

 sliu'htly in size, so that when it enters the thorax (from the abdomen) it 

 becomes reduced to half its former size. As it enters the thorax from 

 behind it plunges downward to just above the oesophagus in advance of the 

 food-reservoir, then passes rapidly upward again to the upper wall of the 

 body, which it follows to the middle of the mesothorax, din.inished again to 

 half its former size, so as to appear a mere thread ; and then, casting free 

 ao-ain, passes forward as in the larva, reaching the oesophagus again in the 

 prothorax in the young chrysalis ; but as it grows older this part bends more 

 and more, until in the mature chrysalis it has completely doubled on its 

 course, running directly downward and backward until the oesophagus is 

 nearly reached and then turns forward parallel to the latter. 



Nervous system. The principal changes which take place during 

 pupation are the enlargement of the cephalic lobes, the shortening of the 

 entire cord, and the concentration of the thoracic ganglia. Between the 

 cephalic and thoracic ganglia the nervous cord in Hamadryas, where we 

 have studied it most attentively, is moderately broad, flattened and double ; 

 the thoracic ganglion, which is a compound of the five ganglia succeeding 



