1922] Branch: Internal Anatomy of Trichoptera 257 



and fuses with the nerve which extends posteriorly from the ganglion 

 situated at union of the nerves from the posterior protuberances of the 

 supra-oesophageal ganglia and the sympathetic ganglia of each side. 



_ From the ventral face of the supra-oesophageal ganglia, arises a 

 pair of connectives, the crura cerebri, which connect the supra-oesoph- 

 ageal ganglia with the sub-oesophageal ganglion. 



Immediately in front of the union of the crura cerebri with the 

 supra-oesophageal ganglia, the oesophageal ring of the tritocerebrum 

 arises. This is a loop which encircles the oesophagus and has its ends 

 connected with the supra-oesophageal ganglia, see Plate XIV, Fig. 5 at or. 

 The supra-oesophageal ganglia does not fit closely upon the oesophagus 

 normally, but leaves some space laterally and ventrally for the expan- 

 sion of the tube in feeding. Faivre 1857, states that the supra-oesoph- 

 ageal ganglia possess the seat of motive power and will power and Binet, 

 1S94, strengthens this statement by the results of his own experiments 

 which show that an insect will live for months with the supra- 

 oesophageal ganglia removed but will not eat unless the food is placed 

 in its mouth as it has no power to move toward the food. 



The sub-oesophageal ganglion is situated slightly back of the 

 posterior margin of the supra-oesophageal and below the oesophagus 

 but well within the limits of the head cavity. This ganglion gives off 

 three pairs of nerves, the most ectal and dorsal of w^hich extends in a 

 forward and upward direction and, upon a level with and in front of the 

 frontal ganglion, branches. One branch extends to the base of the 

 labrum, see Plate XIV, Figs. 5 and 6 at lb2, while a second branch 

 extends to the dorsal side of the mandible, see Plate XIV, Figs. 5 and 6 

 at md2. The second pair of nerves from the sub-oesophageal ganglion 

 arises ventrad of the first pair and extends forward also branching. 

 The ectal branch of each nerve reaches the musculature of the maxilla, 

 mxl; and an ental branch divides and one part goes to the maxillary 

 sclerite and the other to the labium, see Plate XIV, Figs. 5 and 6, at mx2 

 and li2. This pair is connected by a nerve just below the frontal ganglion, 

 and the cross nerve bears a small median ganglion. The third pair of 

 nerves is ventrad of the second pair and extends forw^ard directly to the 

 labium, which it innervates, HI. 



The above description is made from several dozen specimens of the 

 species LimnophUus indivisus Walker. The head ganglia of the other 

 species studied do not vary materially. 



Posteriorly the sub-oesophageal ganglion gives off a pair of com- 

 missures which connect to the first thoracic'^ ganglion lying in the 

 prothorax. In the thorax and abdomen there is much variation among 

 the species as to the relation of the ganglia to their respective seg- 

 ments. Upon observation of these three species {LimnophUus indivisus 

 Walker, Hydropsychodes analis Banks and Phryganea interrupta Say,) 

 two centers of fusion will be found, one in the thorax and one in the 

 abdomen at the posterior end of the chain. As above stated, there are 

 three thoracic and eight abdominal gangHa. The prothoracic and 



* Each ganglion of the thorax and abdomen is a pair of fused ganglia. 



