THE CANADIAN ENTOMOLOGIST 279 



division of the median nerve which has fused with the gangHon. Nerve "A" 

 is the chief nerve of the segment. It passes beneath the major recti muscles, 

 giving off a minor, posterior division, "D", and extends across the tracheae to 

 dorsum, innervating muscles, tracheae and integument. It has several con- 

 nections with the median nerve. Nerve "C" passes backward to unite with a 

 branch from the median nerve of the second abdominal segment, and gives 

 off three main branches, chiefly to the integument. In the segments having 

 prolegs a branch to the proleg of that side is given off from nerve "C" at the point 

 marked "x" on figure 6 of the 2nd ganglion. 



The Eighth Abdominal Ganglion, PI. XI, Fig. 4, possibly represents the united 

 8th and 9th primitive ganglia. The median nerve is found as usual. The 

 first pair, A, are of the normal type, representing the nerves of the primitive 

 connectives and belonging to the 8th ganglion; the pair, "C", probably repre- 

 sent the second pair of the 8th ganglion. They innervate many muscles and 

 the hypoderm of the 8th segment. The last pair, "D", stouter than the others, go 

 to the last two segments of the caterpillar and to the caudal end of the intestine. 

 They give off numerous branches to all the organs of that region, presenting 

 two large ganglia of varying shape in different individuals. 



There is little doubt, from the number of its nerves and its position, that 

 the eighth ganglion in thule is composed of the united eighth and ninth primitive 

 ganglia. Nerves "A" and "C" evidently belong to the primitive eighth ganglion, 

 and nerve "D" would, therefore, represent the fusion of those of the ninth gang- 

 lion. That "D" is a composite nerve has been suggested by DuPorte and it 

 seems probable from its size, extensive branching, and the passage of the vas 

 deferens through it. This last peculiar condition was described by DuPorte in 

 Sphida ohliqiia. It occurs also in thiile but apparently not invariably, since 

 I was unable to demonstrate it in several specimens. In thule the vas deferens 

 normally passes at right angles directly through the middle of a chief branch 

 of the nerve between the two main lateral ganglia. This condition would ap- 

 parently be explained best as resulting from a fusion of the two nerves or two 

 branches of the same primitive nerve. The median nerve of the ninth ganglion 

 has disappeared or fused with "D". 



The Sympathetic System. 



The so-called sympathetic system of insects is usually divided into two or 

 three groups of nerves and ganglia, all of which are very intimately connected 

 with the central system. These are, the Supraintestinal Sympathetic System, 

 comprising the Unpaired Median and the Paired Lateral groups of nerves and 

 ganglia; and the Subintestinal Sympathetic System, or Paired Median Section, 

 comprising the Median Nerves of the ventral chain. In addition to these there 

 is a very delicate network of minute nerve threads and ganglia lying upon the 

 hypoderm, and connected through numerous fine threads with the Central 

 System as well as with the three divisions of the Sympathetic. This has been 

 referred to as the Peripheral or Sensory Sympathetic System. 



The Unpaired Median Section. 



PI. X, Fig. 8. 

 This minor group lies upon the dorsal face of the fore intestine to which 

 its fibres mainly go. It comprises the Frontal Ganglion and the Cephalic and 



