PIG 



RABDIT 



MONKEY 



MAN 



Fig. 23. Comparison of the embryos of the Pig, Rabbit, Monkey, and Man 

 at corresponding stages of development. The embryos of each animal are 

 arranged in the vertical columns according to age, beginning with the youngest 

 stage at the top. Stage A of the human embryo is fully labelled and the cor- 

 responding structures in the other embryos can be noted, a, head region; b, 

 eye; c, ear; d, gill slits; e, heart; f, fore limb; g, primitive muscle segments; 

 h, hind limb; i, tail region. Slightly modified from K. Guenther, after Keibel. 



