696 



ARTHROPODA 



The legs are segmented into the following articles : coxa, trochanter, femur, 

 patella, tibia, and tarsus. 



Internal Anatomy. — The internal anatomy has been studied by Christo- 

 phers in Ornithodoros savignyi, and most elaborately by Bonnet in eight 

 IxodidaB and three Argasidae, males and females. 



The tegument consists of chitinous layers, under which lies the epidermis. 

 On the surface are the openings of numerous glands. A large cephalic gland 

 is present in some species, opening dorsally at the junction of the rostrum 

 with the body. 



The mouth, which is lined with chitin, is situated anteriorly between the 

 mandibular sheath dorsally and the hypostome ventrally. In this position 

 it is merely a horizontal slit, with open sides, but farther back these are closed 

 by the junction of the hypostome with the mandibular sheaths. The cavity 



Fig. 313. — Margaropus annulatus var, australis Say: Distended Female. 



extends backwards some little distance, and ends blindly. Into its postero- 

 lateral angles open the ducts of the salivary glands, two large racemose glands 

 lying over the bases of the first pair of legs. The acini are globular, and their 

 walls consist of large cells, as a rule laden with retractile granules staining 

 deeply, or with indistinct granules staining less deeply. 



In addition to the ordinary acini, there are groups of four or five cells, 

 forming pear-shaped masses, which have a peculiar affinity for acid stains like 

 eosin. These elements are really unicellular glands, which open into the 

 principal salivary ducts, not into the small ductules. These glands, which are 

 numerous in the Argasidae, are probably poison glands. 



On the floor of the mouth is a V-shaped opening, apex pointing forwards, 

 which leads into the pharynx. This is a fusiform organ, narrow in front, 

 where it turns upwards to open into the mouth, while behind it ends in the 

 oesophagus. Its walls consist of chitinous plates arranged ventrally and 

 laterally, so that the lumen is triradiate on transverse section. At the angles 

 the chitinous plates are united together by doubk folds, allowing expansion 



