50 MAN AN ADAPTIVE MECHANISM 



From Haeckel's " Evolution of Man." 



FIG. 4. COMPARISON OF THE EMBRYOS OF MAN AND OTHER VERTEBRATES. 



These pictures are meant to represent the more or less complete agreement, 

 as regards the most important relations of form, between the embryo of Man 

 and the embryos of other Vertebrates in early stages of individual develop- 

 ment. This agreement is the more complete, the earlier the period at which 

 the human embryo is compared with the embryos of other Vertebrates. It 

 is retained longer, the more nearly related in descent the respective matured 

 animals are corresponding to the "law of the ontogenetic connection of 

 systematically related forms." . . . 



"The first, or upper cross-row, I, represents a very early stage, with gill- 

 openings, and without limbs. The second (middle) cross-row, II, shows a 

 somewhat later stage, with the first rudiments of limbs, while the gill- 

 openings are yet retained. The third (lowest) cross-row, III, shows a still 

 later stage, with the limbs more developed and the gill-openings lost. The 

 membranes and appendages of the embryonic body (the amnion, yelk-sac, 

 allantois) are omitted. The whole twenty-four figures are slightly magnified, 

 the upper ones more than the lower. To facilitate the comparison, they are 

 all reduced to nearly the same size in the cuts. All the embryos are seen 

 from the left side ; the head extremity is above, the tail extremity below ; 

 the arched back turned to the right. The letters indicate the same parts 

 in all the twenty-four figures, namely : v, fore-brain ; zz, twixt-brain ; m, mid- 

 brain ; h, hind-brain ; n, after-brain ; r, spinal marrow ; e, nose ; a, eye ; 

 o, ear ; k, gill-arches ; g, heart ; w, vertebral column ; /, fore-limbs ; 

 6, hind-limbs ; s, tail." ^ 



