1917] The Nervous System of Thysanura 305 



shown in the figure and has quite a little depth. The frontal 

 ganglion is not shown in the figure. The first ventral ganglion 

 is large, so are the three thoracic ganglia. There are eight 

 abdominal ganglia differing somewhat in size and somewhat 

 from Oudemans figure. The median ventral nerve was found 

 much as figured by Oudemans. Perhaps the most marked 

 feature was in the backward extension of the optic lobe region 

 because of the position of the eyes. The figure does not agree 

 with Oudemans, largely because the brain is shown in its 

 natural position as it is found in the head. (Figure 3). 



Lepisma resembles Machilis very closely, but because of the 

 more lateral and cephalic eyes the brain is more transverse 

 when viewed from above. The frontal ganglion is shown in 

 the figure. (Figure 4). 



TRACHEAL DISTRIBUTION. 



Trachea can be best studied by removing the ganglia and 

 mounting while still fresh in glycerine. The air in the tracheal 

 tubes remains for a few minutes and the distribution of the 

 trachea may be seen. I found the tracheal distribution much as 

 in the larva of another species. In general, the brain seems 

 supplied by three main trachea on each side. The subesophageal 

 ganglion by two main branches on each side, each ventral 

 ganglion below this with one on each side, but the last ganglion 

 with two branches at least, one of which often has some associa- 

 tion with the branch of the next to the last ventral ganglion. 

 Two branches seems to be the usual number for the last ganglion. 

 (Figure 7-16). 



It was very difficult to study trachea in the small Campodea 

 because it was hard to remove the ganglia in the first place, and 

 second because the trachea remained visible only for a short 

 time. The lower smaller ganglia were each supplied with a 

 single pair of branches, but the supply to the larger cephalic 

 ganglia seemed to be by two sets of main lateral trachea from 

 above and below, each set giving off branches as shown in the 

 figure. The abdominal ganglia are supplied more simply. 

 In none of the centers was there the branching of the tracheoles 

 to the degree found in Evalljapax. 



