INTERNAL ANATOMY. 373 



Nervous System. 



This consists of a double supra-cesophageal ganglion or 

 brain (Fig. 1, b) in the head, an cesophageal collar, a sub- 

 cesophageal ganglion and a row of ganglia extending along 

 the median ventral part of the body cavity. The ventral 

 ganglia are connected by a double commissure (nc). The 

 brain gives off nerves to the ocelli, the sub-cesophageal gan- 

 glion supplies the mouth parts, while from the ventral gan- 

 glia nerves are distributed to the feet, prolegs and internal 

 organs. 



In the caterpillar there are eleven ventral ganglia, includ- 

 ing the sub-o3sophageal. The posterior one is by far the 

 largest, being formed by a fusion of two ganglia. During 

 the pupal stage (Fig. 5) the number of ganglia is reduced 

 by fusion. In the imago we find two thoracic and four 

 abdominal ganglia, which are connected with the brain by 

 a double commissure. 



The Fat Body. 



In its fullest development this body forms an internal 

 cylinder of fat, which surrounds the alimentary canal and 

 lines the body cavity of the caterpillar. It is represented 

 by the dark dotted area in Plate 58, Fig. 2. It is liber- 

 ally supplied with tracheae and is most prominent in well- 

 fed, full-grown caterpillars. In the pupal stage (Fig. 5) the 

 fat body diminishes as the reproductive system develops, the 

 development of the latter taking place at the expense of 

 the former. One fact, which seems worthy of record in 

 this connection, is that almost no fat can be found in the 

 female imago, while there is an appreciable quantity pres- 

 ent in the male. Since the male is the sex that flies, this 

 fat may be necessary to furnish the energy expended in 

 flight. 



Reproductive System. 



This system is represented in the caterpillar by a pair of 

 small reddish-brown organs (Fig. 1, ro), which lie one on 

 each side of the dorsal vessel in the ninth segment. From 

 these organs a pair of thread-like appendages (ducts ?) lead 



