1902.] ANATOMY OP THE PEDIPALPI. 181 



aperture of -the alimentaiy canal at its apex. Its dorsal wall is 

 formed by the horny compressed camarostome. Its ventral wall 

 is an outgrowth of the suboral area of the prosoma, supported 

 posteriorly by a prostei'nal scleiite and by the juxtaposed coxee 

 of the palpi, fused laterally to the camarostome throughout its 

 length ; it thus constitutes a lower lip which eflectually prevents 

 the loss of liquid food, without any share in this office being- 

 taken by any part of the coxte of the adjacent appendages. The 

 special point in which this " beak " resembles that of the Acari is 

 the fact that it foi-ms the sucking-apparatus of the alimentary 

 canal. Otherwise it is unique in the class Arachnida, its parallel 

 being found only in the, in some respects, degenerated Palpigradi. 



That a "beak" of this kind, which is evidently developed in 

 correlation with the long, porrect, and non-retractile cheliceree, 

 was the stai'ting point of the diverse modifications met with in the 

 other orders of Arachnids, seems in the highest degree improbable. 

 Such an hypothesis demands the suppression of the lower lip of 

 the " beak," and its independent replacement functionally by the 

 particular types of suboral trough already described. 



On the other hand, there is no difficulty in regarding all these 

 various kinds of "beaks" as specialized organs resulting from the 

 presence of a camarostome or labrum, and the need for a lower 

 lip or suboral gutter to prevent the loss of nutritive fluids and to 

 guide them into the alimentary canal. 



The muscles of the camarostome in Tlielyphonus, which Bernai'd 

 regards as the beginning of "the sucking-apparatus," seem to have 

 the same function as those of the Scorpion, being, as in tha,t 

 animal, distinct from the suctorial pharynx, which constitutes 

 " the sucking- apjjaratus" par excellence. 



In connection, then, with the anteiioi- portion of the alimentary 

 canal, suckers may be developed in thi-ee distinct places — that is 

 to say, in the camarostome itself, as in the Solifugje, Palpigradi, 

 and Acari ; in the pi'e-cerebiul portion of the foregut, as in the 

 Scorpiones (text-fig. 43, A, B, ph., p. 180), Opiliones, and Pseudo- 

 scorpiones; or in its post-cerebral portion, as in the Aranese, 

 Palpigradi \ and Amblypygous Pedipalpi {Phrymis). 



In the Aranefeand Amblypygi (text-fig. 45, ^:»A., st., p. 186) the 

 pre-cerebral and post-cerebral suckers coexist, and are especially 

 powerful in the former order. In the Palpigradi the post-cerebral 

 sucker is aided in its work by the organ developed in the cama- 

 rostome. In the Scorpiones and Opiliones the pre-cerebral sucker 

 alone is found. In the Uropygous Pedipalpi it is also well 

 developed ; the post-cerebral, on the contrary, is very small as 

 compared with that of the Amblypygi, but the muscles of the 

 camarostome probably aid in the office of suction. The same is 

 true of the Pseudoscorpiones, with the exception that the post- 

 cerebral sucker is absent. In the Solifugpe and Acari the 

 function of suction is apparently performed solely by the muscles 

 of the camarostome. 



1 Rucker, Amer. Nat. xxxv. 1901. 



