6o SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 10 



dorsal plate is widely open at its inner end before the oesophageal 

 aperture (C), but beyond this point the lips are in such close apposi- 

 tion that the channel becomes practically a closed tube (E, dc), except 

 that it opens again where it approaches the mouth (C). On each side 

 of the median channel the surface of the plate is crossed by numerous 

 fine ridges. 



A longitudinal section of the dorsal pharyngeal plate of Tegenaria 

 domestica (CI.) (fig. 21 F), as given by Bartels (1930), shows that 

 the surface ridges are high, thin folds of the cuticle, most of them 

 forked along their free edges, between which are deep grooves. The 

 grooves, Bartels believed, open mesally into the dorsal channel, though 

 he was not able to demonstrate the apertures. In experiments on 

 spiders allowed to drink water containing a suspension of India ink 

 or carmine particles, he found the granules massed in the grooves 

 and along the edges of the median channel, but very few in the channel 

 itself, while only some of the smallest particles had gone into the 

 stomach with the water. From these experiments Bartels concluded 

 that the ridges of the pharyngeal plate constitute a filtering apparatus 

 for the retention of undissolved material in the predigested food, 

 while the liquid part enters the oesophagus by way of the grooves 

 and the dorsal channel of the pharynx. The main lumen of the 

 pharynx, according to Bartels, serves for the discharge of the diges- 

 tive juices that first liquefy the soft tissues of the prey. However, 

 inasmuch as with other arachnids the food is ingested through the 

 pharynx lumen, it might be supposed that the dorsal channel of the 

 Araneida serves as the conduit for the exuded digestive liquid ; the 

 very fact that the grooves of the dorsal plate become so readily 

 clogged would seem to disqualify them as food conduits. A dorsal 

 channel of the pharynx is present, however, also in the Phalangiidae, 

 which are not known to practice extraoral digestion. 



The musculature of the araneid pharynx includes the usual dilators 

 arising on the epistome (fig. 21 A), and muscles attached on its upper 

 end. It is shown by Brown (1939) that in Agelena naevia (A) there 

 are two pairs of long dorsal muscles from the carapace, and a pair 

 of ventral muscles from the pedipalp sternum, all attached on the 

 upper end of the pharynx. The first dorsal muscle Brown calls a 

 dilator of the pharynx, the second a retractor ; the ventral muscle he 

 terms a retractor of the "labium." Within the labrum are two trans- 

 verse muscles (tmcls) as in most other arachnids. 



The oesophagus curves downward and again upward from the 

 pharynx (fig. 21 A, B, D), and expands to form a proventricular 

 pump (A, D, PvP) before reaching the stomach. The oesophagus 



