Vol. X, No. 10.] Indian Spiders. 417 



[N.S.] 



of them situated a little on the outer side of the middle of 

 the whole row. 



The highest type of stridulating organ known to me is that 

 found in C. stridulans (pi. xxxi, fig. 6)- In this the palpal por- 

 tion of the organ consists almost entirely of the ventral row 

 of large claviform bacilli, the largest of which in this species 

 are on the inner, not the outer side of the middle; and the 

 portion situated on the chelicerae consists not of spines but of 

 stout denticles. 



In all other species known to me the organ is of the 

 stridulans type, or intermediate between this and the assamensis 

 type. The portion of the organ situated on the chelicerae 

 always consists of denticles, not spines, but the extent of the 

 relatively small dorsal bacilli on the coxae of the palps differs 

 in different species. The position of the stoutest bacilli also 

 varies in different species, and may possibly indicate a poly- 

 phyletic origin for the genus ; but in the present state of our 

 knowledge it is not possible to discuss this further. 



There still remain the Ornithoctoneae and the Poecilo- 

 therieae to be considered. In neither case is any clear evidence 

 of their origin available. The t} 7 pe of stridulating organ found 

 in the Ornithoctoneae resembles that found in the Thrigmo- 

 poeeae; but there is no evidence to show that the latter ever 

 existed north or east of the Indian Peninsula, or that the 

 former ever existed north or west of Burma. So it is probable 

 that the two originated independently. 



The stridulating organ of the Poecilotherieae, a group 

 consisting of the single genus Poecilotheria, somewhat resembles 

 that of ChilobrachySy but could only be derived from it by 

 a considerable degeneration of the claviform bacilli. It could 

 be more directly derived from Selenocosmia; but there is 

 no evidence that Selenocosmia ever occurred in the Indian 

 Peninsula, or that Poecilotheria ever occurred out of it. 

 Indeed, if the former genus had ever entered this Peninsula 

 it might be expected to occur there more abundantly than 

 further east, just as the Ischnocoleae do ; and if the latter had 

 originated further east it is difficult to see, in view of its 

 peculiar habits, by the competition of what other group it 

 could have been exterminated there. The labium of Poecilo- 

 theria, moreover, is sparcely denticulate, not closely granular. 

 Most probably, then, Poecilotheria originated from the Ischno- 

 coleae or Thrigmopoeae (or both) in the Indian Peninsula 

 itself, the modified habits of its earliest arboreal ancestors 

 having been in some way correlated with an increase in the 

 potentiality of these ancestors to give rise to forms more 

 highly specialized than themselves. This increase has carried 

 the group far beyond the stage reached by the highest of the 

 Plesiophrictus-Thrigmapoeus series, in a direction largely paral- 

 leled, so far as the stridulating organ is concerned, by the evo- 



