84 
AV. F. rUECELL. 
equally readily over and over again in the Arachnida^ and 
particularly in so large and diversified an assemblage as 
the Tracheata? Thus in the Solifugfe the thoracic 
trachem, which open at the base of the third pair of legs and 
have always been an unexplained anomaly in view of the 
branchial theory,^ may easily have originated from the entapo- 
physes of some muscle. The same remark applies to the 
occurrence of the remarkable pair of tracheal spiracles dis- 
covered by Hansen (’93, p. 198), and subsequently confirmed 
by Loman (’96) on the tibiae of the four pairs of legs in the 
Phalangii dae." 
I do not mean to imply that these abnormal tracheae were 
must, in fact, be Ijetter adapted for their purpose than the hmg-book 
tracheae.” This remark of Pocock's may possiidy explain why such 
highly segmented forms as the Solifugmhave highly developed trachea; 
only, since the extraordinary activity of the members of this group 
would require the iJi’esence of the most effective breathing organs. 
Bernard ('90, p. 374) mentions that these are the only Arachnids in 
which the primitive tracheal tubes anastomose (as in the Insecta), 
and to this I may add an observation which I have often made on living 
Solpngidse, which is that regiilar and pronounced respiratory 
movements are observable in the middle part of the body, especi- 
ally after the animal has been running. Similar movements have not 
hithei’to, so far as I am aware, been recorded for any air-breathing 
Arachnids (see Plateau, '86). 
' Bernard ('92, p. 521), for instance, remarks that the presence of 
trachea; on the cephalothoi’ax in Arachnida is “one of the principle 
difficulties in the way of those who would deduce the Arachnidan abdo- 
minal trachea; from embedded gills. ... It compels us, for instance, 
to assume that the cephalothoracic ti-achea; have had an entirely dif- 
ferent origin, so that . . . it is necessary to assiune that the same 
strncBires, tubular ti-achea;, have had two independent origins in the 
same animal! . . . there is absolutely no difference between the 
trachea; which open through the large stigmata of the thorax and those 
opening tlu’ongh the more insignificant stigmata in the al)domen [in 
the Solifuga;]. It is difficult to believe that they had a separate 
origin. The embedded gill theory must, I think, definitely give way 
before some simpler theoi'y, such as that here put forward.” So also 
Weissenborn ('87, p. II4). 
- It is interesting to note that Loman foiind these spiracles absent in 
very young Phalangii da;. 
