762 Charles Paul Alexander 



The nervous system 

 The most important literature on the nervous system is as follows: 



Ptychoptera. Grobben, 1876. 



Dicranota. Miall, 1893:241. 



Phalacrocora. Miall and Shelford, 1897:350; Bengtsson, 1897. 



Ctenophora. Anthon, 1908:556-557. 



Holorusia. Comstock and Kellogg, 1904:58-59. 



In Holorusia the brain, or supra-esophageal ganglion, is composed of 

 two principal lobes united posteriorly and lying above the esophagus. 

 Beneath the brain and on the under side of the esophagus lies the sub- 

 esophageal ganglion, which is connected with the anterior end of the 

 brain lobe by the circum-esophageal commissures. The above-named 

 organs form a complete ring, or collar, around the alimentary canal. The 

 ventral nervous system leads backward from the subesophageal ganghon 

 on the ventral surface of the body wall. In the thorax there are four 

 closely approximated ganglia representing the thoracic and the first 

 abdominal segments. Beyond these and located in the abdomen are 

 six abdominal ganglia. The ganglia send off four large nerve trunks. 



The condition is similar in Ctenophora and in Tipula, there being seven 

 abdominal gangha, of which the first is located in the thorax and the last 

 six in the abdomen. In Phalacrocera there are eight abdominal ganglia, 

 the first being usually found in the first abdominal segment and the 

 eighth in segment 10. The head ganglia are all independent of one 

 another, not fused into a complex. The longitudinal commissures between 

 the first five ventral ganglia are double, and those between the eight 

 abdominal ganglia are simple (Bengtsson). In Dicranota there are like- 

 wise eight abdominal ganglia, the first being located in the first al^dominal 

 segment and the others in segments 5 to 10, there being two close together 

 in the tenth segment. 



The reproductive system 

 The most important literature on the reproductive system is as follows: 



Ptychoptera. Grobben, 1876. 



Dicranota. Miall, 1893:248. 



Phalacrocera. Miall and Shelford, 1897:356-357. 



Holorusia. Comstock and Kellogg, 1904 : 58. 



The reproductive organs appeiar early in the larval development. In 

 Dicranota the testes lie in the ninth segment and form elongate capsules, 



