312 Annals Entomological Society of America [Vol. X, 



5. Cells of various sizes send fibers into the mass of the 

 ganglion. 



6. The longitudinal fibers to the connectives may be found 

 in every part, but they are not always evident because of the 

 many fine fibrils from various regions all woven in with them. 



SOME GENERAL CONCLUSIONS. 



The nervous systems of the four genera studied show some 

 similarities but many differences. The general position and 

 number of the ganglia is quite similar. Campodea, the least 

 specialized in most respects, has one less ventral ganglion. The 

 general shape of the four brains are quite different, even those 

 without eyes are not alike and those with eyes have them so 

 differently connected with the brain that the whole arrange- 

 ment of the nervous system at this point is altered. Nerve 

 cells differed chiefly in size and minor arrangements. The 

 largest animals had the largest nerve cells. The general course 

 of fibers and fibrils could be traced but special tracts were not 

 traced very far. The general areas of mushroom bodies were 

 determined for all. Only in Lepisma were these structures 

 well developed, in Machilis and to a less degree in Campodea 

 condensations of fibrils were taken to indicate them. 



The general distribution of tracheal vessels is as follows: 

 The brain has three main branches on each side, the sub- 

 esophageal ganglion two branches from each side, the thoracic 

 and abdominal ganglia as a rule have one branch each on a 

 side and the last abdominal ganglion has usually two branches 

 on each side. The brain of Campodea was not easily removed, 

 so that the condition there was not so clearly made out, but 

 the appearance so far as could be told was as stated for the rest. 

 The thoracic and abdominal ganglia, however, have a distribu- 

 tion which is not like the rest. Possibly the long lateral trachea 

 on either side with its branches to the ganglia may represent 

 a more primitive if not an absolutely different condition. For 

 this and other reasons I am inclined to think of Campodea 

 separated from the other genera by a wide gulf. Japax seems 

 separated from the rest by the next widest gulf. 



The segregation of fibrils in clumps means a closer union 

 in some places than others; this probably means: 1. Fibrils 

 are closely massed that go in the same direction. 2. In some 



