ANATOMY. 608 



search has hitherto been completely unsuccessful. I 

 have not observed any pulsating organ whatever. 



When we consider the very rudimentary state of the 

 organ in the Gamasidce, and the extreme activity of 

 that family of Acarina, it is not improbable that it may 

 be absent altogether or quite rudimentary, in such 

 lethargic creatures as the Orihatidce. 



The Nervous System. 



In vol. i, at p. 184, it was mentioned that I had not 

 then been able to trace the nervous system of the 

 Oribatidoe except so far as regarded the great sup ra-oeso- 

 phageal ganglion, the so-called brain ; nor have I been 

 much more successful since. I have found the nerves 

 of these minute and inactive creatures very difficult to 

 demonstrate with any certainty, and I have not suc- 

 ceeded in finding any stain or reagent which will 

 differentiate them from the surrounding tissues. One 

 observation may be worthy of record. I have satisfied 

 myself that in Oribata globula a chain of at least three 

 small roundish ganglia, joined to the supra-oesophageal 

 ganglion and to each other by fine commissures of 

 moderate length, runs from each side of the supra- 

 oesophageal ganglion ; and is directed toward the side 

 of the body and then downward and backward ; the 

 first is smaller than the second. This chain is repre- 

 sented, somewhat diagrammatically, on PI. LIII, 



I have observed similar ganglia in Pelojps but did 

 not succeed in detaching them so as to trace the com- 

 missures. 



I have also ascertained that a nerve does run to the 

 inner end of the pseudo-stigmatic organ (PI. XLVIIa, 

 fig. 8), but I cannot say whence it comes. 



