426 ARACHNIDA SOLIFUGAE CHAP. 



shown by Bernard l to be due to the enormous development of the 

 chelicerae, by the muscles of which they are entirely occupied. 



The floor of the cephalothorax is for the most part formed 

 by the coxae of the appendages, and the sternum is hardly re- 

 cognisable in many species. In Solpuga, however (see p. 429), it 

 exists in the form of a long narrow plate of three segments, end- 

 ing anteriorly in a lancet-shaped labium. 



A pair of large simple eyes are borne on a prominence in the 

 middle of the anterior portion of the cephalothorax, and there are 

 often one or two pairs of vestigial lateral eyes. 



The first pair of tracheal stigmata are to be found behind the 

 coxae of the second legs. 



The mouth-parts take the form of a characteristic beak, con- 

 sisting of a labrum and a labium entirely fused along their sides. 

 The mouth is at the extremity of the beak, and is furnished with 

 a straining apparatus of complicated hairs. 



The abdomen possesses ten free segments, marked off by dorsal 

 and ventral plates, with a wide membranous lateral interval. 

 The ventral plates are paired, the first pair forming the genital 

 opercula, while behind the second and third are two pairs of stig- 

 mata. Some species have a single median stigma on the fourth 

 segment, but this is in some cases permanently closed, and in the 

 genus Rhagodes entirely absent, so that it would seem to be a 

 disappearing structure. 



The appendages are the six pairs common to all Arachnids 

 chelicerae, pedipalpi, and four pairs of legs. The chelicerae, 

 which are enormously developed, are two-jointed and chelate, the 

 distal joint being articulated beneath the produced basal joint. 

 In the male there is nearly always present, on the basal joint, a 

 remarkable structure of modified hairs called the " flagellum," and 

 believed to be sensory. It differs in the different genera, and is 

 only absent in the Eremobatinae (see p. 429). The pedipalpi are 

 strong, six-jointed, leg-like appendages, without terminal claw. 

 They end in a knob-like joint, sometimes movable, sometimes 

 fixed, which contains a very remarkable eversible sense-organ, 

 which is probably olfactory. It is concealed by a lid-like struc- 

 .ture, and when protruded is seen to be furnished, on its under 

 surface, with a pile of velvet-like sensory hairs. 



The legs differ in the number of their joints, as the third and 



1 Trans. Linn. Soc. (2), vi., 1896, p. 310. 



