THE SECOND ORDER OF ARACHNIDES. 
THE TRACHEAN (TRACHEARLE), 
Differ from the preceding, in the respiratory organs con- 
sisting of radiated or ramified tracheae, and not receiving the 
air but through two apertures or stigmata; in the absence of 
a circulatory organ ; and in the number of eyes, which is but 
from two to four. From the want of anatomical observations 
sufficiently general, the limits of this order are not yet rigor- 
ously traced. Even some of these arachnides, such as the 
pycnogonides, present no stigmata, and their mode of respira- 
tion is unknown. 
The trachean arachnides are very naturally divided into 
those which are provided with forceps terminated by two 
claws, one of which is mobile, or by one alone, likewise 
mobile, in the form of a talon, or hook ; and those in which 
these organs are replaced by simple lamina), or lancets, 
and which, with the tongue, constitute a sucker. But most 
part of these animals being very small, this examination in- 
volves great difficulties, and we feel that such characters 
should not be employed but when we find it impossible to do 
without them. 
The first family of Trachean Arachnides, that of 
Pseudo Scorpiones, 
Has the thorax articulated, with the anterior segment much 
