3/2 THE EVOLUTION OF MAN. 



almost the entire chest-cavity (Fig. 123, o-v). Behind it the 

 very small rudiments of the lungs lie concealed. The 

 primitive kidneys are very large (Fig. 123, m), occupying 

 the greater part of the ventral cavity, and extending from 

 the liver (/) to the pelvic intestine. Thus at the end of 

 the first month, all the essential parts of the bod}' are 

 already begun; and yet, in this stage, we are still unable 

 to discern any characters essentially distinguishing the 

 human embryo from those of the Dog, the Rabbit, the 

 Ox, the Horse, or, indeed, of any of the higher Mammals. 

 All these embryos are still of the same form, and at best 

 differ from the embryo of Man only in the general dimen- 

 sions of the body, or in the size of the individual organs 

 differences of no moment. Thus, for example, the head, 

 relatively to the trunk, is a little larger in Man than in the 

 Sheep ; in the Dog the tail is somewhat longer than in 

 Man. But these are all, evidently, very trifling differences 

 indeed, and of no importance. On the other hand, the 

 whole internal and external organization, the form, the 

 disposition, and the connection of the separate parts of the 

 body of the germ are essentially the same in the human 

 embryo of four weeks, and in the embryos of other 

 Mammals in a corresponding stage of development. 



But the case is different even in the second month of 

 human development. Fig. 122 represents a human germ, 

 VI., of six weeks, VII., of seven weeks, VIII., of eight 

 weeks, in the natural size. The differences which distin- 

 guish the human embryo from those of the Dog and the 

 lower Mammals, now gradually begin to become more 

 prominent. Even after the sixth, and yet more after the 

 eighth week, considerable differences are visible, especially 



