SOME ANALOGIES AND HOMOLOGIES. 93 



Our limbs form beautiful subjects for comparison. Throughout 

 the vertebrates they never exceed four in number. They are all 

 modifications of one type, whether we take the fins of fish, the 

 wings and legs of birds, fore and hind legs of quadrupeds, or arms 

 and legs of man. Comparing the leg of a bird with the leg of a 

 man, we see that the complete leg of a bird shows first the thigh 

 bone, then the tibia or lower leg bone, and then in the place of the 

 tarsus and metatarsus a single bone, with, at its lower extremity, a 

 small bone supporting the four toes. Primarily the analogy be- 

 tween the last five bones of the bird and the so-called tarsus, 

 metatarsus, and toes of man does not seem very complete, but if 

 the chick in the egg, be examined, its leg will be found to consist 

 of the thigh bone, of the tibia, of two tarsal and three or four 

 metatarsal bones, and the toes or jjhalanges. The upper tarsal 

 bone subsequently becomes anchylosed with the tibia and the 

 lower one with the consolidated metatarsus. Now the analogy 

 becomes much more complete. 



The horse has but a single metatarsal bone (the third), with 

 rudiments of the second and fourth. These rudimentary meta- 

 tarsal bones of the horse are very interesting. By means of them 

 it is comparatively easy to trace out his descent. I may be par- 

 doned for mentioning such well-known facts and analogies as the 

 following, among the vertebrata that the whale possesses the 

 rudiments of hind legs, that the boa constrictor possesses also 

 the rudiments of a leg and a pelvis, and that the rudiments of 

 the wings are discoverable in the apteryx. 



A few other animal analogies: The third eyelid of the bird 

 exists also in some amphibians and reptiles and in sharks ; also in 

 man as a rudimentary structure. 



The manner in which cows, deer, and sheep tear up the grass 

 when they are feeding, plucking away at the tufts, is familiar to 

 any observant man. The incisors of the upper teeth are wanting. 

 The interesting analogy is the fact that the teetb are really there, 

 but they are uncut that is to say, they have never pierced the 

 gum. 



The skin with its appendages forms a beautiful story of analogy. 

 Our own microscopical epidermic ^ scales are. strictly comparable 

 with the cells that liiqike tip i^hfe^ajes of 9sh a^d of reptiles ; their 

 further development/ into' tralrS and, nj^ils again compares with 

 the feathers of birds and't'h liooT?. arid 'horns of animals. 



We call ourselves a hairless i-acs; but everywhere on our bodies 

 are the small lanugo hairs.: ',"gi,i4tauiaticm'will readily cause these 

 hairs to grow to any exte:ai"' The ' sal rgebn has frequent oppor- 

 tunities of witnessing this retrograde progression toward a lower 



type. 



Molting has its analogy throughout the animal kingdom. We 



