92 TRANSFORMATIONS OF THE 



ered by most authors as a pumping stomach, by 

 the exhaustion of which the fluids pass up the 

 spiral tongue ; but we have found that other organs 

 exist sufficient for this purpose, and it seems more 

 probable that it is either a simple air vesicle, 

 rendering the insect more buoyant, or a food res- 

 ervoir, wherein to store and digest at leisure the 

 honeyed sweets obtained on a sunny day. The 

 salivary glands and malpighian vessels do not 

 greatly change in character during the growth of 

 the insect [Pig. 79, on page 82]. 



The respiratory and circulatory systems differ 

 so little in the larval and perfect stages of butter- 

 flies that it is not worth while to dwell upon 

 them. It may simply be remarked with refer- 

 ence to the latter that the dorsal vessel has (1) be- 

 come less vague, with well-defined vascular walls 

 and regular and considerable periodic enlarge- 

 ments ; and that (2) in the thorax it does not fol- 

 low the superior wall of the body throughout, but 

 near the middle, where it enlarges considerably, it 

 returns upon itself, plunging downward and back- 

 ward through the mass of muscles which fill the 

 chest until it has nearly gained the point at which 

 it entered the thorax ; when it turns once more 

 toward the head and passes to it in a nearly 

 straight course. 



The nervous system has greatly altered, al- 

 though its general course and structure remain 



