38 JOURNAL OF ENTOMOLOGY AND ZOOLOGY 



of the gauglia. Auotlier point wliicli is equally interesting is 

 the small size of the nerve cells. The small size of the animal 

 antl the consequent smaller number of nerve cells as compared 

 witli larger insects, is apparently not the only difference be- 

 tween this insect and those of larger size. Most of the nerve 

 ceils of Aphorura are aliout two or two and a half microus in 

 diameter. They are much smaller than other cells of the body, 

 even smaller, in fact, than the nuclei of certain cells, such for 

 example as the epithelial cells of the intestine. 



The details of structure of the nervous system will not be 

 considered at this time, but a In-ief description will be given of 

 the ganglia and the chief branches of the nerve centers of the 

 head region. The larger ganglia of tlie animal are disposed 

 much as shown in Fig. 37, i)l. XII, of Philiptschenko's work. 

 However he shows no supraesophageal ganglion in this figure 

 and the position of some of the caudal parts of the nervous 

 system differs from the corresponding portions of Aphoniia. 



In Aphorura the supra- and subesophageal ganglia are large 

 and joined together liy broad connectives in their forward por- 

 tions. A section across these ganglia at such a level shows 

 them as one mass with the small esophagus in a little opening 

 in the center of this mass. The connections between the sub- 

 esophageal ganglion and the first thoracic are not as close as 

 between the two large head ganglia. 



There are three large thoracic ganglia about opposite each 

 pair of legs. These are joined together by broad and short 

 connectives. Beyond the third thoracic ganglion and broadly 

 connected with it, is a thick mass which represents the fused 

 abdominal ganglia. This extends into the abdominal region a 

 short distance and ends in a nerve which probably supjilies 

 most of the al)dominal organs. I found no ganglia below this 

 point but there were some indications of nerve cells where there 

 were no distinct ganglia. 



The large abdominal mass broadly fused to the last thoracic 

 center, was found on median sections, to show evidences of being 

 composed of several fused ganglia. 



