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 equi. A degenerate Spider or mite, parasitic on the skin of the 



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- 



