The Bird 



F.E. 



turns to the right (in ourselves, the left-side gill-channel 

 forms this aortic arch), is what is left of the fourth pair 

 of aortic gill-arches, while the two arteries which, in aH 

 higher animals, leads to the right and left lungs, are the sel> 

 same channels which in the creatures of olden time encircbd 

 the sixth pair of gill-bars. 



Although the eye of the bird is far superior to thaf of 



a fish in seeing abiity, 

 yet in actual structure 

 there is not very nuch 

 difference, except that 

 the bird has gained 

 eyelids, tear^lands, 

 and a few other struc- 

 tures. Fishe-, frogs, 

 lizards, bins, and 

 mammals, tlrough all 

 the ages, Iwe depend- 

 ed on thesJ two eyes 

 and have found them 



FIG. 369. Pineal eye in Chick (P. E.). 



all-sufficirfit; but there 

 are hin# that once, 

 long ago, the ancestors of all the higher animls had a sense- 

 organ, probably of sight, situated, like thafof the mythical 

 Polyphemus, in the centre of the head, In lizards this 

 vestigial organ is sometimes quite well Developed, having 

 a nerve which leads up from the centr of the brain to a 

 kind of translucent, lens-like scale wJch lies among the 

 other scales of the skin, upon the cerre of the forehead. 

 In the long-extinct Ichthyosaurs this^edian eye was prob- 



