ANATOMY OF ARACHNIDS 



17 



With the twelve neiiromeres of the suboesophageal ganghon 

 these five paired evanescent gangha in the abdomen make up 

 the usual number of seventeen for group I of the arachnids, 

 which may here be tabulated. 



Cephalo- 

 thorax 



ABDOMINAL GANGLIA 



Scorpions 



Ambl ypygi 



Thelyphonides 



Tartarides 



Spiders 



1 1 1 

 

 



1112 

 







6 segments 



(11111) 



(Transient) 



7 segments 5 segments 



GROLP II. VII. 80LIFUGAE AND PALPIGRADES 



The Solifugae being tracheate animals, there are no blood 

 channels to divide the neuromeres, although in the cephalo- 

 thorax their place seems to be taken to some extent by tracheae. 

 By means of the tracheae and the nerves proceeding from the 

 suboesophageal ganghon, one can determine that the suboeso- 

 phageal ganglion is composed of five neuromeres supplying ap- 

 pendages II to VI. The nerve supply to appendage Yl, on 

 which the racquet organs are situated, is very abundant, and is 

 supplemented by a number of secondary ganglia at the roots of 

 the racquets themselves. 



With the neuromeres supplying appendage \l, however, the 

 suboesophageal ganglion appears to come to an end, and from 

 this point there is a large nerve cord leading into the anterior 

 p^rt of the abdomen where it swells into a large single ganglion 

 in the region of the genital segment. The nerve cord emerges 

 from this ganglion posteriorly, and can be traced a short dis- 

 tance after which it becomes distributed into small filaments 

 and gradually disappears. There is no trace of any ganglion 

 in the abdomen other than the one mentioned, nor does this 

 ganglion show any evidence of being divided into neuromeres. 

 It is simply one solid ganglionic mass (diagram 6, fig. 1). 



JOURNAL OF MORPHOLOGY, VOL. 29, NO. 



