VI ARAGHNOIDEA— INTESTINAL CANAL 523 



belong to the category of coxal glands. In TromUdium a gland with its opening lies 

 on the terminal joint of each leg. 



Glands of the pedipalps (the 2d pair of extremities) have been observed in various 

 Arachnoidea (Atypus and other Araneidm, Solpugiclce, Scorpimiidce, Phalangidce, and 

 Tetranyckiis among the Acaridce). They have been classed somewhat arbitrarily, 

 some as salivary glands, others (Galeodes) as poison glands, and others again as spinning 

 glands (Tetranychas). 



Grlauds emerging on the chelioerae are also somewhat widely distributed. The 

 best known and most investigated are the poison glands of the Araneidae, which 

 mostly lie in the cephalo-thorax, but often partly project into the chelicerae themselves 

 and always open outward on their terminal claws. In the Gamasidce also there are 

 glands at the bases of the chelicerje. According to recent observations, the webs pre- 

 pared by the Pseudoscorpionidce are said to be formed by glands lying in the 

 cephalo-thorax, whose ducts penetrate into the chelicerie and open on the terminal 

 joint. Earlier observers had asserted that the spinning glands and their apertures 

 were to be found on the ventral side of the first abdominal segment. In the 

 Linguatulidm there are glands emerging at the bases of the 4 clinging hooks. 



We thus find in the Arachnoidea a striking number of limb glands. This number 

 will no doubt be stfll further increased on more thorough investigation, and it may 

 perhaps be established, that many of these glands, especially those emerging on the 

 coxal joints of the extremities, belong, like the spinning glands of the Armwidm, to the 

 category of segmental coxal glands homologous with the setiparous glands of the 

 Annelida. 



2. Glands not emerging on the Limbs. — Here belong the integumental glands 

 emerging through pores in the chitinous cuticle at various parts of the surface of the 

 body ; these have been observed in diflferent divisions, with special frequency, however, 

 in the Acaridce and Linguatulidce, and have been called oil glands, stigmatic glands, 

 stink glands, etc. The poison gland of the Scorpion also belongs to these. It is 

 paired, lies in the swollen terminal segment of the post-abdomen and emerges by 2 

 separate apertures at the point of the sting with which the tail is armed. In the 

 Phalangidoe and OyphopMhalmidm (Gibbocellum) there is in the cephalo-thorax one pair 

 of glands (the so-called Krohn's glands), the 2 ducts of which are said to emerge 

 through 2 apertures on the dorsal side of the cephalo-thorax. 



V. The Intestinal Canal. 



This has as a rule a straight course through the body. We can 

 again distinguish in it the three well-known divisions, fore-gut, mid- 

 gut, and hind-gut. 



The Fore-gut. — The mouth or buccal cavity is followed by the 

 muscular pharynx, which functions chiefly as a suction pump, as 

 it can be expanded by means of special groups of muscles attached 

 to it, and contracted by circular muscles. The pharynx passes into 

 the narrow oesophagus. This passes through the oesophageal ring and 

 enters the mid-gut. Before entering the latter it swells, in the Aran- 

 eidm, into a special sucking stomach. 



The mid-gut forms by far the largest portion of the digestive tract. 

 In the Arachnoidea it shows in a very high degree the tendency to 

 form eoecal invaginations which surpass all the rest of the viscera 

 taken together in size and importance. Where the cephalo-thorax and 



