182 



TARSAL-COMB IN SPIDERS. 



such variations, and the explanation of the use of a rudimentary 

 organ. Natural selection, as propounded by Dr. Darwin, does 

 not pretend to account for the rudiments of organs, though, once 

 set going, the future progress and perfection of them is easy 

 enough to understand, and although Dr. Wallace conclusively 

 proves the extreme variability of living organisms, rendering it 

 impossible to predict in what direction a development may take 

 place, yet this does not quite account satisfactorily for the fact 

 that these developments appear to take place just exactly where 

 they are needed ; unless we suppose that the psychical forces 

 embodied by an organism are ready on the slightest hint from 

 without, through the media of nerve fibres, to force a development 

 in the line suggested by peculiarities of environment. 



Fig. 1. — Apical portion of the tarsal joint of the fourth pair of legs 

 of a female Therldion tepidariorum, showing three of the 

 spines of the tarsal comb at D, the two superior claws at A, 

 the central inferior claw at B, and a pair of auxiliary claws 

 at C. 



Fig. 2. — Represents the extremity of one of the spinesi shown at D, 

 in Fig. 1, exhibiting the barb-like emarginations. 



At Fig. I, may be seen the apical three of the nine spines of 

 the tarsal comb, D D D, with their characteristic curve and 

 barbs ; while at A may be observed the two normal tarsal claws, at 



