170 CALIFORNIA ACADEMY OF SCIENCES. 



of the alimentary canal. In others, however, they are 

 straight. In Menopon titan they form V-shaped tubes 

 with the bend forward and the inner arm joining the 

 intestines. Each tube consists of an apparently struct- 

 ureless investing membrane (plate xi, fig. 6), of a single 

 layer of large granular epithelium cells within this, and 

 finially of a thin intima lining the epithelium. The 

 lumen is narrow and irregular since the inner ends of 

 the cells are angular, and a convexity on one side of the 

 lumen fits into a concavity of the epithelium on the 

 opposite side. 



III. The Respiratory System. 



The trachese are disposed in two main trunks, one on 

 each side of the body, reaching from the posterior end 

 of the abdomen into the head. Spiracles are situ- 

 ated laterally on the dorsal side of the abdominal seg- 

 ments, and in some species, as Menopon titan, there is a 

 spiracle on each side of the prothorax (See Kellogg, 

 1896). A short branch connects each spiracle with the 

 main longitudinal trunk of the same side. Opposite the 

 union are given ofT several branches to the various 

 organs of the body. In the head the lateral trunks 

 end by dividing into numerous branches. No dilatation 

 of the tracheae occurs at any point. In Menopon titan 

 a large transverse trunk connects the two lateral trunks 

 in the fourth abdominal segment. 



IV. The Nervous System. 



The nervous system consists of a brain and sub- 

 cesophageal ganglion in the head and a large ganglion 

 in each of the thoracic segments. From the two head 



