XVI ANATOMY A27 
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 cephalothorax and the 
abdomen there is no true pedicle, but there is a transverse 
septum or “diaphragm,” through which the blood-vessel, tracheal 
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 with innumerable 
secondary tube-like diverticula, which proceed in all directions 
and fill 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 off an 
anterior and a posterior vessel, the latter apparently a vein, as it 
is guarded at its entrance by a valve. The blood seems to be 
delivered by the anterior artery on to the nerve-mass, and, after 
percolating the muscles and viscera, to divide into two streams— 
the one returning to the heart by the thoracic ostia, the 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. 
