THE SECOND ORDER OF ARACHNIDES. 



THE TRACHEAN (TRACHEARI^), 



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 



