GENERAL CLASSIFICATION AND STRUCTURE. 



23 



Palps. 



rotary motion upon the fore part of the sternum, moving toward and 



against each other, thus crushing the interposed prey. 



The palps (ps) or palpi are two organs inserted into the free end of 



the maxilla-, of which they are an organic part. 1 Each palp has five 

 joints of various lengths named in order from the maxilla, (1) 

 axillary, ax, (2) humeral, hu, (3) cubital, cu, (4) radial, ra, and 



(5) digital, dg. The axillary joint is the shortest of the five and corre- 

 sponds to the second joint of the leg or trochanter, the maxilla being the 



equivalent of the coxa. 2 The 



humeral joint is much longer 



than the axillary; the cubital 



again is short, being a sort of 



knee joint. The radial is one 



and a half or twice as long as 



the above, and the digital is 



usually the longest joint of all. 3 

 The palps vary greatly in 



the two sexes. In the female 

 each digital, dg, ter- 



Sexual m i na tes like the foot 

 Forms of -, . ^ -> 



p , and is usually armed 



with a well developed 

 curved claw (palpal claw) pec- 

 tinated or serrated. These or- 

 gans are prehensile, are used va- 

 riously as hands or feet to hold 

 and turn the prey, to dig, to 

 sustain the body when suspend- 

 ed Upon Webs, to grasp the CO- FIG. 12. Male of Agalena ncevia : the speckled Tubeweaver. 



coon, etc., and even to aid in (Marx, del.) 



locomotion. In the male the digital joint contains the genital organ ; it is 

 enlarged, often very greatly, into a bulb whose structure is complicated and 

 subject to great specific variations. (Fig. 12.) It is always more or less 

 covered on top by a plate, which may be distinguished from other parts 

 by a more or less dense pubescence scattered upon the superior surface and 



1 On account of the curved process upon the top of each maxilla whose convexity is 

 toward its fellow, the palp may be said to issue from the side instead of the end of the 

 maxilla. 



2 Westrinw. " Aranese Svecia?," Termini Technici, page 11. 



3 I have adopted the terminology of Walckenaer, which is followed also by Blackwall 

 and Cambridge. That of Westring is (in the same order as above) : (1) basal, (2) femoral, 

 (3) patellar, (4) tibial, (5) tarsal. The analogy between this terminology and that of the 

 legs, perhaps has some advantage to the memory, but the Walckenaer names appear to me 

 to be preferable, as being quite distinctive, and thus preventing confusion with names given 

 to the joints of the legs. 



