INTERNAL ANATOMY. Ill 



ganglion the nerve arises from. Croneberg, speaking of 

 Eylais extendens, one of the Hydrachnidas, says that the 

 palpal nerves arise from the sub-oesophageal ganglion.* 



Schaub, speaking of Hydrod/roma, also one of the 

 Hydrachnidse, considered that the palpi were inner- 

 vated from the supra-oesophageal ganglion. f 



With regard to the nerves proceeding from the 

 supra-oesophageal ganglion, I was able in one happy 

 median sagittal section of Hericia Rolnni to trace 

 clearly the azygous pharyngeal nerve (PL C, fig. 1, npli) ; 

 although possibly I might not have detected it had I 

 not been so well acquainted with it in some other 

 Acari, and looked for it. It is a very fine nerve 

 arising from the median point of the anterior end of 

 the supra-ossophageal ganglion almost close down upon 

 the oesophagus ; it follows a straight line along the 

 dorsal surface of the anterior end of the oesophagus, 

 and sends out fine nerve-threads which innervate the 

 dilator and occlusor muscles of the pharynx. I cannot 

 say that I was able to trace to my own satisfaction the 

 course or destination of any of the other two or three 

 pairs of nerves which may just be seen arising from 

 the supra-ossophageal ganglion. Nalepa considered 

 that he had traced two pairs, the first he says inner- 

 vate the mandibles (Chelicerse) and the second the 

 palpi. With regard to the first I have no doubt that 

 Nalepa is right ; because in all Acari, where I have 

 been able to trace the nerves with certainty, the man- 

 dibular nerves have arisen from the supra-oesophageal 

 ganglion, and this is usual in adult Arachnoidea. It 

 may be said that the mandibular nerves of insects arise 

 from the sub-oesophageal ganglion ; this, however, is 

 subject to three remarks, viz. (1) that many writers, 



* "On the Anatomy of Eylais extendens, Miiller, with Observations 

 on Allied Forms," in Russian in * Mem. Soc. Moscou,' 1878. A short 

 summary in German called " Ueber den Bau der Hydrachniden," in 

 ' Zool. Anz.,' 1878, No. 14, p. 316. 



t 

 ir 

 Abth. i (1888), p. 98. 



" Ueber die Anatomie von Hydrodroma (C. L. Koch) : ein Beitrag 

 zur Kenntniss der Hydrachniden," in ' S. B. Ak. Wien,' Bd. xcvii, 



