THE ORIGIN OF SPECIES 



355 



gous. Moreover, the appendages of the Crayfish are not only 

 serially homologous among themselves, but are also homolo- 

 gous with the appendages of all the other members of the 

 class Crustacea just as the limbs of one Vertebrate are 

 homologous with those of all other Vertebrates. 



Another class of facts presented by comparative anatomy 

 is derived from the so-called VESTIGIAL organs. In Man 

 there are nearly a hundred structures which at best are 

 useless and sometimes are harmful. One thinks at once of 

 the VERMIFORM APPENDIX of the large intestine, a remnant 

 of an organ which serves a useful purpose in the vegetable- 

 feeding (herbivorous) Mammals. (Fig. 88.) But equally 

 suggestive are the muscles of the ear, which in some indi- 

 viduals are sufficiently developed to move the external ear; 

 the so-called third eyelid at the inner 

 angle of the eye which corresponds 

 to the lid (NICTITATING MEMBRANE) 

 that moves laterally across the eye 

 in Bird and Frog; or the terminal 

 vertebrae (COCCYX) of the human 

 spinal column which are remnants 

 of the tail of lower Vertebrates. 

 (Fig. 87.) 



Other animals are likewise replete 

 with such structures. Porpoises 

 possess vestiges of hind-limbs en- 

 closed within the body, and cer- 

 tain species of Snakes have tiny use- 

 less hind-legs. The 'splint bones'. of 

 the Horse are remnants of lost toes. 



Among plants, it will suffice to mention the functionless 

 remnant of the pistil which sometimes is present in 'male' 

 (staminate) flowers. (Figs. 166, 187, 189.) 



Fia. 187. Vestigial hind- 

 limbs of a Snake, Python, f, 

 femur or thigh bone; il, ilium 

 or hip bone. (From Romanes.) 



