50 THE BUTTERFLIES OF NEW ENGLAND. 



segment of the abdomen, the heart narrows slightly, making the beginning 

 of" the aorta. This after entering the thorax runs upwards, passing between 

 the right and left sets of thoracic muscles, and then under the suture l)e- 

 tween the mesoscutum and scutellum, and expands rather suddenly into a 

 large [aortal] chamber, which is hung in })osition by a net-work of fibrous 

 connective tissue. . . . The forward end [of this] bends downwards [some- 

 times abruptly] and again contracts into a [more or less] slender tube [in 

 Hesperians scarcely slenderer than the aortal chamber, but compressed] , 

 which runs backward and downward until it reaches the first j>art of the 

 aorta, and after passing along the anterior face of this for a short distance, 

 it bends suddenly forward and runs along, and just above, the oesophagus, 

 passing with the latter into the head and through the oesophageal nerve 

 collar" (Burgess). The aorta then divides into several branches, which 

 are lost in the integuments of the head. 



Nervous system. A brain, a compound thoracic ganglion, and four 

 abdominal ganglia, lying along the ventral wall of the body and connected 

 by double, often connate commissures, form the base of the nervous system 

 in butterflies. 



The brain occupies the centre of the head, immediately over the oesoph- 

 agus, is laterally bilobate and principally made up of two enormous optic 

 nerves. It furnishes also the antcnnal nerves and is connected by short 

 cords on either side to a minute frontal ganglion, which gi\es off poste- 

 riorly a recurrent nerve ; there are also a pair of posterior, lateral, minute 

 eanolia in the head connected ^\■ith this recurrent nerve, which inner\ates 

 the oesophagus and dorsal vessel and v.ith its branches spreads over the 

 stomach. The commissures which extend from the brain backward pass 

 on either side of the oesophagus and immediately before leaving the head 

 unite beneath to form the suboesophageal ganglion ; from this arise the 

 nerves which pass to the mouth parts. 



The thoracic ganglia are situated in the front part of the mesothorax, 

 and separated by a considerable distance from the ganglia of the head. 

 They are compound, and their compound origin is usually marked to some 

 extent by the form of the mass itself, but they sometimes form a single 

 elongated oval disc. From this arise the crural and alary nerves, or those 

 su[)plying the legs and wings. 



The abdominal ganglia, small round lenticular discs, are always four in 

 num1)er, the first separated from the thoracic ganglion by a distance of 

 nearly half the length of the entire nervous cord, the last compound ; they 

 are situated in the third to the sixth abdominal segments respectively and 

 are equidistant. As the cord enters the abdomen, and for the rest of its 

 course, it becomes bordered right and left by a white fibro-muscular mem- 

 brane, which fixes it to the -ventral tegument according to Dufour ; and 

 the same writer states that a white ellipsoidal fibrous capsule is embraced 



