A CHAPTER IN DARWINISM 



31 



seen still to possess the eight walking legs, small, it is 

 true, whilst the palps and daggers of the spider have 

 dwindled to a beak projecting from the front of the 

 globular unjointed body. In the other the eight legs 

 have become mere stumps, and the body is elongated 

 like that of a worm. 



Fig. 11. 



Fig. 12. 



Fig. 11. — Acarus eqiii. A degenerate Spicier or mite, parasitic on the skin of tlie 



horse. 



Fig. 12. — Degenerate Spider (Demodex folliculorum) found in the skin 



of the human face. 



The instances of degeneration which we have so 

 far examined are due to parasitism, except in the ex- 

 ample of the Barnacle, where we have an instance of 

 degeneration due to sessile and immobile habit of life. 

 We may now proceed to look at some sessile or im- 

 mobile animals which are not usually regarded as de- 



