hitroduction to Animal Morphology. 



365 



Fig. 43- 



temporary depressions, which have been mistaken for 

 stigmata. The segments ofthe limbs are built on the 

 Crustacean type, but the full series of seven are rarely 

 developed. In some parasitic Mites the foot is dis- 

 coidal. Oribates has postero-lateral dermal folds, like 

 the mantle of Entomostraca, or the wings of Insects. 



The mouth is often surrounded by a lip-like swell- 

 ing, and armed with the antennary jaws, which are 

 strong, hollow, with an opening on their inner side, 

 into which the duct of a poison gland (the homologue 

 of the shell gland of Crustaceans r) opens. In this 

 duct are spiral muscular fibres, which squeeze out the 

 poison. In Solpugidae the first pair of 

 feet becomes masticatory or prehensile. 

 Salivary glands exist in the higher 

 forms. Two pair of lobed glands are 

 present in Scorpions, two convoluted 

 pouches in Galeodes, several pair of 

 small sacs in some Mites.* In Aca- 

 rines the mouth is suctorial. There is 

 rarely a pharynx, and the oesophagus 

 is narrow, thick, sometimes with a 

 chitin-lined longitudinal groove open- 

 ing into the stomach, which is long, 

 with its anterior part (stomach proper) 

 elongated into caeca, which enter the 

 limbs. Such caeca are two, rudimen- 

 tal in Scorpions and Phrynidae, five 

 pair in Spiders, entering the limbs and palpi. In 

 Mygale the hinder pair branch and anastomose. In 



Digestive Canal of 

 Spider : n, nerve ring 

 around oesophagus ; 

 c, ca:-ca from the sto- 

 mach ; /, liver ducts ; 

 r, cloaca, with two 

 linear urinary tubes 

 opening- into it (out- 

 side /). 



* It is not easy to unravel the connexion between the poison gland of 

 the antennae and the salivary glands in spiders, but they seem to be quite 

 separate. 



