22 THE BUTTERFLIES OF NEW ENGLAND. 



the second thoracic segment, where there are no spiracles, are small and 

 comparatively inconspicuons, and connected with the bnncli in the first 

 abdominal segment behind by only a small longitudinal canal. The first 

 thoracic segment, which has a spiracle and generally one of larger size than 

 usual, bears, however, an extensile bunch of tracheae. The anterior branch 

 of tliis bunch supplies the head ; it arches upAvard on each side along the 

 hinder edge of the head, until it meets that of the opposite side, when the 

 two join so strongly that consideral)le force is required to part them ; and 

 the only mark of se})aration is a pale line on the dusky surface. As soon 

 as they meet, they bend toward the head, then separate and run side l)y 

 side beneath the muscular mass which occupies most of the head, over the 

 double cephalic ganglion and curve over toward the lab rum. Before unit- 

 ing, these two opposite branches emit from their anterior surface similar 

 branches, which also run beneath the muscular mass toward the anterior 

 and lower [)art of the head ; some curve upward and embrace the muscu- 

 lar mass from below ; half way between the spiracle and the top of the 

 head this first-mentioned arching branch emits from its posterior surface a 

 slender offshoot, which, together with another branch, coming almost direct 

 from the spiracle, pass toward the tracheae of the opposite side, and unite 

 at the median line with a similar set from the opposite trachea. 



Circulatory system. The circulatory system consists mainly of the 

 "dorsal vessel," — a straight tube, lying along the middle of the back, next 

 the skin ; it seems to be composed externally of an excessively fine whit- 

 ish pellucid film. It is of varying shapes, simple and uniform in Anosia, 

 ending in a well-rounded ti}) at the extremity of the body ; as slender as 

 the nerAOUs cord as far as the middle of the third abdominal segment in 

 Ilamadryas ; but beyond this point, where it is attached to the wall of the 

 Ijody, it suddenly expands to a nuicli larger size, and retains the same as 

 far as the seventh abdominal segment ; here and in the next segment it 

 expands into a fusiform reservoir and then tapers to the end of the body : 

 in Callophrys it is comparatively large and equal as far as the third ab- 

 dominal segment, though it expands slightly at the point of attachment of 

 the salivary glands near the middle of the thoracic region. The dorsal 

 Acssel is very elastic and ficxible, and when one side is pulled even pretty 

 forcibly the other remains in place. It is seen to be slightly enlarged at 

 the division lines of the segments marking the ends of the chambers, where, 

 by the refiection of the tissues, a valve-like structure is formed, hj which 

 the fluids are forced from one chamber into the next, the movement being 

 from Ijchind forward. 



Nervous system (86:1). The nervous system of butterfly larvae con- 

 sists of a scries of horizontal disks, connected by a straight slender double 

 ribbon, emitting lateral threads, and which runs along the floor of the 

 internal ca\ity from the head, where it extends upward, encircles the 



