l6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 10 



and the pedipalp coxae (B, ecAp), on apodemes of the coxae, or on 

 the coxal walls. 



The sucking organ of the arachnids, with its dorsal dilator muscles 

 arising on the epistome, is suggestive of the sucking pump of liquid- 

 feeding insects, with its dilator muscles arising on the clypeus. Fur- 

 thermore, the organ in each case is anterior to the frontal ganglion 

 and its brain connectives. The frontal ganglion of the arachnid lies 

 on the dorsal surface of the oesophagus (fig. 2 F, FrG), but since 

 the oesophagus {Oe) penetrates the central nerve mass, the ganglion, 

 as shown by Holmgren (1920) and by Hanstrom (1928), is buried 

 within the surrounding tritocerebral lobes of the brain (F, /G). 



The usual sucking organ of the insects, with dilator muscles from 

 the clypeus, is not the pharynx ; it is a derivative of the preoral food 

 cavity, while the true pharynx is a part of the stomodaeum and lies 

 behind the frontal ganglion. The sucking organ of the arachnids 

 is usually said to be the first part of the stomodaeum, and is therefore 

 called the pharynx. According to Wagner (1894), however, the suck- 

 ing apparatus as developed in Ixodes is a secondary invagination added 

 to the primary stomodaeal invagination, "ein neues Theil des Stomo- 

 deums, welcher die Aniage fur den Saugapparat bildet," the walls 

 of which become hardened and give attachment to the dilator muscles. 

 The primary stomodaeal invagination, Wagner says, forms the narrow 

 oesophagus. There is therefore reason to believe that the so-called 

 pharynx of the arachnids is a secondary derivative of the preoral 

 cavity, as is the preoral cibarial sucking pump of the insects. Though 

 the arachnid organ is usually well differentiated in structure from the 

 functional preoral cavity, it is in some cases, as in the Thelyphonidae 

 and Araneida, practically continuous with the latter, and in the Chelone- 

 thida most of the dilator muscles arising on the epistome are inserted 

 on the dorsal wall of the preoral cavity. To avoid confusion with 

 current nomenclature, however, we may continue to call the sucking 

 organ of the arachnids the "pharynx." 



The oesophagus is always a narrow tube, which, after leaving the 

 pharynx, traverses the central nerve mass on its way back to the 

 mesenteron. Just before entering the latter it usually enlarges to form 

 a small second, proventricular sucking organ, the so-called "stomach 

 pump," or "Saugmagen." 



Comparison of Arachnida and Xiphosurida. — A comparison of the 

 arachnids with the xiphosurids shows that there is little in common 

 between the two groups with respect to the feeding organs or the 

 method of feeding. In the Xiphosurida the coxae of the first five 

 pairs of postcheliceral appendages have large spiny mesal lobes op- 



