PULMONARIJE. 335 



the volatile alkali, used externally and internally. There are several 

 species. 



ORDER II. 



TRACHEARI^E. 



The Arachriides which compose this order differ from those of 

 the preceding one in their organs of respiration, which consist of 

 radiated or ramified tracheae(l), that only receive air through two 

 stigmata; in the absence of an organ of circulation; and in the num- 

 ber of their eyes, which is but from two to four. The want of suffi- 

 ciently general anatomical observations, has prevented the limits of 

 this order from being rigorously determined. Some of these 

 Arachnides, the Pycnogonides for instance, exhibit no stigmata; 

 their mode of respiration is unknown. 



The Trachearias are very naturally divided into those which are 

 furnished with chelicera3, terminated by two fingers, one of which is 

 movable, or by one that is equally so; and into those where these 

 organs are replaced by simple laminas, or lancets, which with the 

 ligula constitute a sucker. Most of these animals, however, being 

 very small, great difficulties necessarily accompany these investiga- 

 tions, and it is readily perceived that such characters should only be 

 resorted to when it is impossible to avoid it. 



FAMILY I. 



PSEUDO-SCORPIONES. 



In this family we find the thorax articulated, its first segment much 

 the largest, and resembling a corselet; the abdomen is very distinct 

 and annulated, and the palpi very large and in the form of legs or 

 claws. There are eight legs with two equal hooks at the extremity 

 of the tarsi, the two anterior ones, at most, excepted, and two appa- 



(1) The trachea are vessels which receive the aerial fluid and distribute 

 it to every part of the interior of the body, and thus remedy the want of 

 circulation. 



