UnO] . The Palpi of Male Spiders 165 



the genital bulb is nearly terminal but is, nevertheless, distinctly 

 on one side of the tarsus (Fig. 3). In other spiders it has moved 

 to a greater or less extent towards the base of the tarsus, which 

 it has nearly reached in many, as for example in Loxosceles 

 rufescens (Fig. 4). It has been suggested by Nelson ('09) that 

 this shifting of the position of the bulb is for the protection of 

 it from mechanical injury. 



In Hypochilus (Fig. 3) and in Loxosceles (Fig. 4), the alveolus 

 is comparatively small; but in many spiders it is large, resulting 

 in the tarsus being more or less cuplike in form; this is shown in 

 some of the figures of the more specialized palpi given later. 

 This cuplike form of the tarsus as distinguished from its appen- 

 dage, the genital bulb, suggested for it the name cymbiiim 

 (Menge '66), which is the classical name of a small drinking 

 vessel. The term lamina, proposed by Westring ('61) antedates 

 cymbium; but I have adopted the later term, as it is the one 

 in general use. 



The well-known fact that tarsal claws do not exist on the 

 palpi of male spiders is easily understood if we regard the 

 genital bulb as a specialization of the tip of the palpus, as is 

 indicated by the structure of the palpus of Filistata described 

 above. Sometimes, as in Lycosa, the tip of the cymbium bears 

 one, two, or three stout spines; these have been regarded as 

 "transformed claws" (Chamberlin '08); it seems more probable 

 for the reason given above, that these are secondarily devel- 

 oped structures instead of vestigial claws; in fact there are fre- 

 quently strong spines distributed over the surface of the cym- 

 bium. 



The genital bulb in Filistata is helicoid; this is due, so far as 

 the larger basal part is concerned, to the fact that the wall of 

 it is molded over the coiled receptaculum seminis; but the 

 twisting of the bulb is continued to the tip of the embolus, 

 although in this part, the receptaculum seminis is not coiled 

 but extends in a nearly direct line. I know of no other case 

 where the helicoid form of the genital bulb is so well-marked 

 as here ; but there is always a more or less spiral arrangement of 

 parts. 



The Tarantula Type of Palpus. — In those spiders that 

 are commonly known in this country as tarantulas, and which 

 represent the more generalized of the two principal divisions of 

 the order Araneida, there exists a comparatively simple type of 



