NO. lO IKKIUNG OKGANS OF AKAClIMUA — SNODGRASS 5I 



in the stomach, and the final digestive processes take place intra- 

 cellularly within the stomach diverticula as with other arachnids. 



Kiistner (1925), in dcscri})ing the observed manner of feeding by 

 Flatyhuuus coruigcr Herm. on a spider, says the captured prey is held 

 in the chclicerac, and the abdomen first torn open. Then, while one 

 of the pincers holds the cut edge, the other reaches into the opening 

 and pulls out pieces of the entrails and brings them to the mouth parts. 

 The fragments are seized by the coxal endites of the pedipalps and 

 first legs, which open and close alternately and pass the food on to 

 the mouth. After the meal, Kristner observes, both the chelicerae and 

 the pedipalps, which latter have assisted in the act of feeding, are 

 cleaned by drawing them through the oral lobes. 



IX. THE .XR.WETDA 



The spiders possess several features in the feeding apparatus by 

 which they dift'er from the other arachnids. The two-segmented 

 chelicerae have usually no process opposing the fanglike terminal 

 segment, which closes against the basal segment. In all families ex- 

 cept the Uloboridae the chelicerae contain poison glands. The pedi- 

 palp coxae, except in Liphistiidae and most of the Mygalomorphac, 

 have large distal processes usually forming strong but immovable 

 jawlike lobes. The lower lip, or floor of the preoral food cavit}-, is 

 formed by the sternum of the pedipalp segment, which may be either 

 free Ix^tween the pedipalp coxae, or united with the sternal plate of 

 the legs. The dorsal and ventral walls of the pharynx are more or less 

 sclerotized, forming a strong dorsal plate and a more weakly developed 

 ventral plate, the two connected laterally by membranes. The dorsal 

 plate is traversed by a median channel running forward from the 

 orifice of the oesophagus. The proventriculus is a strongly developed 

 pumping organ, the so-called "stomach pump," and may be of more 

 importance in the sucking function than the pharynx itself. 



The cheliceral poison gland is a sacklike organ (figs. 19 A, 20 F) 

 with a duct traversing the fang to open on the convex side of the 

 latter near the point (fig. 19 A, VPr). In the Mygalomorphac the 

 gland is contained entirely or mostly within the basal segment of the 

 chelicera ; in other groups it may project into the body cavity as far 

 as the prosomatic nerve mass or beyond it. The gland is covered by 

 a layer of muscle fibers: the fil)ers are said by Millot (1931) to be 

 generally arranged spirally along the length of the sack, but to present 

 variations and irregtilarities. In Lotrodcctus vxactans. the highly 

 venomous "black widow" spider, the mu.scles, as shown by Reese 

 1944), run longitudinally on the gland (fig. 20 F). 



