xvi ANATOMY 427 



fourth pairs have the femora divided, and the tarsus jointed. 

 The first pair has only a very small terminal claw, but two well- 

 developed claws are borne by the tarsi of the other legs. Each 

 of the last legs bears, on its under surface, five " racket-organs," 

 believed to be sensory. 



Internal Structure. The alimentary canal possesses a suck- 

 ing chamber within the beak, after which it narrows to pass 

 through the nerve-mass, and after an S-shaped fold, joins the mid- 

 gut. This gives off four pairs of thin diverticula towards the legs, 

 the last two entering the coxae of the third and fourth pairs. 



At the constriction between the cephalo thorax and the 

 abdomen there is no true pedicle, but there is a transverse 

 septum or "diaphragm," through which the blood-vessel, trachea 1 

 nerves, and alimentary canal pass. The gut narrows here, and. 

 on entering the abdomen, proceeds straight to a stercoral pocket 

 at the hind end of the animal, but gives off, at the commence- 

 ment, two long lateral diverticula, which run backwards parallel 

 with the main trunk. These are furnished witli innumerable 

 secondary tube-like diverticula, which proceed in all directions 

 and till every available portion of the abdomen. The caeca, 

 which are so characteristic of the Arachnidan mid-gut, here reach 

 their extreme development. A pair of Malpighian tubules enter 

 the main trunk in the fourth abdominal segment. 



Other excretory organs are the coxal glands, which form many 

 coils behind the nerve-mass, and open between the coxae of the 

 third and fourth legs. They have been taken for poison-glands. 



There is a small endosternite in the hinder portion of the 

 cephalothorax under the alimentary canal. 



The vascular system is not completely understood. The heart 

 is a very long, narrow, dorsal tube, extending almost the entire 

 length of the animal, and possessing eight pairs of ostia, two in 

 the cephalothorax and six in the abdomen. It gives oil' an 

 anterior and a posterior vessel, the latter apparently a vein, as it 

 is guarded at its entrance hy a valve. The Mood seems to lie 

 delivered by the anterior artery on to the nerve-mass, and, niter 

 percolating the muscles and viscera, to divide int.. t\\o streams- 

 the one returning to the heart by the thoracic ostia tin- other 

 passing through the diaphragm and bathing the abdominal 

 organs, finally to reach the heart either by the abdominal ostia 

 or by the posterior vein. 



