308 ARACHNIDA. 



of numerous articulated segments, terminated in the scorpion tribe 

 by a sharp unciform sting (fig> 140), armed with a venomous se- 

 cretion. 



The third section embraces the AIIANEID^E, or Spiders, distin- 

 guished by having the abdomen short and globular, and furnished, 

 moreover, near its posterior termination with spinnerets, by means 

 of which these animals manufacture silken filaments applicable to a 

 great number of purposes, and especially employed in constructing 

 what is usually named the spider's web. The maxillary palpi in 

 the females are simple, and more or less resemble feet ; but in the 

 males they often form a remarkable apparatus, to be described in 

 another place : the jaws are also armed with sharp and hooked fangs, 

 and perforated near their points for the emission of a poisonous 

 secretion provided for the destruction of their prey. 



(353.) Beginning with the first cfivision, we shall now proceed 

 to place before the reader such facts as have been ascertained, con- 

 nected with the anatomical structure of the class under considera- 

 tion. In the Acaridse, or Mites, the skin of the entire body is so 

 soft that any annulose structure is scarcely distinguishable; the 

 division, however, into cep halo-thorax and abdomen is sufficiently 

 evident. The eyes are minute black points, never exceeding four 

 in number and resembling the ocelli of insects. Eight feeble legs 

 are articulated with the thorax, properly so called. The mouth 

 seems adapted to suction, and the jaws form a piercing instrument 

 barbed at the extremity. The structure of the respiratory stig- 

 mata or spiracles would seem to differ very considerably from those 

 of insects. According to Dr. Auduoin, in the species which he 

 examined (Ixodes Erinacei),* each spiracle resembles a spherical 

 tubercle perforated by an infinite number of small holes, in the 

 centre of which may be remarked a larger circular plate ; and it 

 is through these numerous foramina that the air enters the body, 

 and gets into the tracheae. 



(354.) The Pulmonary Arachnidans, both of the pedipalp and 

 spinning divisions, are strictly carnivorous in their habits, living 

 upon the juices of the insects they destroy; and we may consequent- 

 ly expect, in the construction of their alimentary apparatus, a sim- 

 plicity proportioned to the facility with which highly nutritive food 

 composed of already anhnalized materials is capable of being assi- 

 milated. The mouth varies somewhat in its conformation, and, if 

 we compare the pieces composing it with those that we have found 



* Cyclop, of Anat. and Phys. art. ARACHNIDA. 



