ORGANIC EVOLUTION 31 



statement that the higher animals Hving today have 

 the original adult stages telescoped into their em- 

 hrvos, and the statement that the resemblance be- 



FiG. 15. — Cleavage stages of four types of eggs; a, 

 Planarian; 6, Annelid; c, Mollusc (Crepidula); d. 

 Mollusc (Unio). 



tween certain characters in the embryos of higher 

 animals and corresponding stages in the embryos of 

 lower animals is most plausibly explained by the as- 

 sumption that they have descended from the same 

 ancestors, and that their common structures are em- 

 bryonic survivals. 



