ORGANS OF DIGESTION. 355 



XII. Arachnida. The carnivorous character of the 

 arachnida is indicated by the shortness and straightness of 

 their alimentary canal, and by its small capacity, as well as 

 by the poison-instruments with which they are often furnished, 

 and by the imperfect development of their chylopoietic 

 glands. They prey chiefly upon living insects, which their 

 cunning instincts, and their offensive weapons enable them to 

 ensnare and to overcome, and many parasitic species suck the 

 living fluids from the surface of higher animals. The mouth 

 of the arachnida, like that of insects, is furnished with a pair 

 of strong articulated mandibles, which are here often per- 

 forated near the point for the transmission of a poison-duct, 

 as seen in the spiders. The mouth is likewise furnished with a 

 small pair of palpigerous maxillae, a labium or inferior lip, 

 and a lingua. The pharynx of the spiders leads to a short 

 oesophagus, on which there are two pairs of small proven- 

 tricular sacs, opening together into the same part of the 

 canal, and which sometimes have the form of elongated 

 follicles. The oesophagus continues narrow from this multiple 

 crop, through the cephalo-thorax to the large abdominal 

 cavity, which is chiefly filled with the biliary lobules and 

 with the genital organs. The intestine here forms a small 

 round stomach, and continues straight to the anus at the 

 posterior end of the trunk, exhibiting a small dilatation or 

 colon before it terminates. The palpi in the male spiders 

 end in a wide oval bulb, containing the sexual organ, and 

 in the female the terminal joint of the palpi is slender and 

 elongated. In the parasitic acari the palpi are simple pedi- 

 form extensions of the maxillae, as in the spiders, and do not 

 terminate in prehensile pincers, like the large palpi of the 

 scorpions. There are several distinct follicular salivary 

 glands in the trombidium and other genera, which pour their 

 secretion into the mouth, like the two salivary glands of the 

 scorpions. The maxillae and tongue sometimes form a 

 lengthened piercing and sucking proboscis, as in sucking 

 insects. In the simpler tracheated species, the mouth ap- 

 pears sometimes to open by distinct orifices on both sides of 

 the head, and their small stomach is furnished with numerous 

 biliary follicles. The anal portion of the intestine in the 

 spiders receives the secretion of several urinary follicles, 

 which terminate in a small sac. or bladder, before opening 



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