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Selecting the Vertebrates again as an example, the high- 

 est form of mammal e.g., man presents in his earliest 

 stages of embryonic growth a skeleton of cartilage, like 

 that of the lamprey : he also possesses five origins of 

 the aorta and five slits on the neck, both which charac- 

 ters belong to the lamprey and the shark. If the whole 

 number of these parts does not coexist in the embry- 

 onic man, we find in embryos of lower forms more 

 nearly related to the lamprey that they do. Later in 

 the life of the mammal but four aortic origins are found, 

 which arrangement, with the heart now divided into two 

 chambers, from a beginning as a simple tube, is charac- 

 teristic of the class of Vertebrates next in order the 

 bony fishes. The optic lobes of the human brain have 

 also at this time a great predominance in size a char- 

 acter above stated to be that of the same class. With 

 advancing development the infant mammal follows the 

 scale already pointed out. Three chambers of the 

 heart and three aortic origins follow, presenting the 

 condition permanent in the batrachia ; and two origins, 

 with enlarged cerebral hemispheres of the brain, resem- 

 ble the reptilian condition. Four heart-chambers, and 

 one aortic root on each side, with slight development of 

 the cerebellum, follow all characters defining the croco- 

 diles, and immediately precede the special conditions 

 defining the mammals. These are, the single aorta 

 root from one side, and the full development of the 

 cerebellum : later comes that of the cerebrum also in 

 its higher mammalian and human traits. 



Thus we see the order already pointed out to be true, 

 and to be an ascending one. This is the more evident 

 as each type or class passes through the conditions of 

 those below it, as did the mammal ; each scale being 



