4-52 LECTURE XIX. i 



leg-like instruments into which the maxillary and labial palpi are 

 converted. 



The Saltatores have the terminal joint of the palpi abundantly 

 beset with hairs, and use them to brush off dust or other extraneous 

 matters from the anterior eyes : requiring distinctness of vision to 

 make their sudden springs available in seizing their prey. 



The alimentary canal is short and straight in most Arachnids : a 

 slight convolution of the intestine takes place in some spiders : that 

 of mites is straight and wide, but the stomach, in some which have 

 the anus near the middle of the abdomen {Erythreus), is produced 

 into lateral sacculi ; these are bifurcated in Ixodes. In the Pycno' 

 gonidce the long and slender gastric caeca penetrate the chelicera, and 

 the eight long and slender legs, as far as the end of the tibia. In 

 scorpions, the alimentary canal extends, without any gastric dila- 

 tation or intestinal convolution, from the mouth to the anus. Five 

 short and straight diverticula are sent off at equal distances from 

 each side of the thoracic portion, and are lost in the granular and 

 seemingly adipose masses, which have been regarded as a kind of 

 epiploon by some, by others as an hepatic organ. Two delicate 

 capillary renal tubes unite on each side, close to the intestine, and 

 open into that part of the canal which is in the anterior part of the 

 tail-like abdomen. 



The spiders are remarkable for the minuteness of the pharynx and 

 oesophageal canal. Savigny believed that in some species there 

 existed three pharyngeal apertures, through which the juices, ex- 

 pressed from the captured insect by the action of the maxillary plates 

 {fig- 165, n) were filtered, as it were, into the narrow oesophagus. 

 In the Mygale, however, there is certainly but one aperture : this is 

 defended above by a horny plate, or rudimental labrum ; below by 

 the labium, which is soldered to the plastron in the Mygale, but 

 jointed and movable in most of the smaller spidei's. 



The pharyngeal fissure {fig. 165, b) ascends between an anterior 

 convex plate or palate and a posterior concave plate, both of which 

 are shed and renewed at each moult. The slender oesophagus passes 

 backwards at a right angle to the pharynx, perforates the nervous 

 ring, and expands into the stomach (ib. d). In the house-spider 

 {Tegenaria domestica), the gastric cavity is produced into four sacs, 

 which are susceptible of great distension when a large prey is cap- 

 tured. In another species of spider (Pholcus rivulatiis), the oesophagus 

 {fig. 166, a), having passed under the brain (c), suddenly expands 

 into a stomach, almost as broad as the sternum, which sends off a 

 long clavate ca3cal process into the base of the maxillary palpi (e), 

 and of each thoracic leg {e'). A shorter diverticulum (</) is continued 



