238 THE ROYAL SOCIETY OF CANADA 



Nerve B arises from the side of the ganglion, near the posterior 

 end. It takes a posterior lateral course, passing beneath the recti 

 muscles. The proximal branch a is a minute nerve which runs for- 

 ward to the suture, innervating the anterior portion of the segment. 

 Branch b is given off near the origin of a and divides into three main 

 branches which again divide, innervating the ventral surface of the 

 segment. The third branch c arises about 1 mm. distad of the origin 

 of b. It runs inward and backward and divides into three branches, 

 one of which runs back and joins the transverse nerve of the next 

 segment ; the others innervate ventral diagonal muscles. Nerve B 

 continues its lateral course and forks near the main tracheal trunk. 

 The branches go to the lateral transverse muscles, traveling in close 

 connection with the tracheal branches. 



Nerves of the Second Abdominal Ganglion. (Fig. 1, II). 

 Nerve A. This nerve is homologous with the corresponding nerve of 

 the first abdominal ganglion but differs somewhat in the distribution 

 of its branches. The first branch a is given off from the posterior side 

 of the nerve, about -8 mm. from the ganglion; running obliquely 

 backward, it joins a branch of the tracheal system and follows it to 

 the under side of the ventral recti majores. About -8 mm. distad 

 of the origin of a, branch b arises. This nerve has been traced to one 

 of the branches of the tracheal system and to one of the lateral oblique 

 muscles. In some cases a and b have been found to originate as a 

 single branch of nerve A. 



Laterad of the origin of b, a short branch connects nerve A with 

 a stout unbranched nerve (fig. 1, o.n.) which is attached near the 

 anterior conjunctiva of the ventral side of the segment and runs 

 obliquely across the segment beneath the muscles, the other end being 

 attached near the posterior conjunctiva of the dorsum. This peculiar 

 nerve, which I have called the oblique nerve, resembles the longitudinal 

 nerve in appearance and its dorsal attachment is not far from the 

 posterior attachment of the latter. Both of these nerves need farther 

 study. 1 



The fourth branch, d, of nerve A goes to the lower transverse 

 muscles. The next branch is a cross-nerve between nerve A and the 

 transverse nerve. This cross-nerve gives off a branch, r, which in- 

 nervates the retractor spiraculi. 



The farther distribution of this nerve is practically the same as 

 that of the corresponding nerve of the preceeding segment. 



Nerve B does not differ essentially from the posterior nerve of the 

 first abdominal ganglion and therefore need not be described sep- 

 arately. 



1 It is possible that these nerves represent chordotonal organs. 



