The Theory of Evolution 71 



at one end, — the gastraea. He dignified the recapitulation 

 theory with an appellation of his own, " The Biogenetic 

 Law." Haeckel's fanciful and extreme application of the 

 older recapitulation theory has probably done more to bring 

 the theory into disrepute amongst embryologists than the 

 criticisms of the opponents of the theory. 



In one of the recognized masterpieces of embryological 

 literature, His's " Unsere Korperform," we find the strongest 

 protest that has yet been made against the Haeckelian 

 pretension that the phylogenetic history is the "cause" of 

 the ontogenetic series. His writes : " In the entire series of 

 forms which a developing organism runs through, each form 

 is the necessary antecedent step of the following. If the 

 embryo is to reach the complicated end-forms, it must pass, 

 step by step, through the simpler ones. Each step of the 

 series is the physiological consequence of the preceding 

 stage and the necessary condition for the following. Jumps, 

 or short cuts, of the developmental process, are unknown in 

 the physiological process of development. If embryonic 

 forms are the inevitable precedents of the mature forms, 

 because the more complicated forms must pass through the 

 simpler ones, we can understand the fact that paleonto- 

 logical forms are so often like the embryonic forms of to-day. 

 The paleontological forms are embryonal, because they have 

 remained at the lower stage of development, and the present 

 embryos must pass also through lower stages in order to 

 reach the higher. But it is by no means necessary for the 

 later, higher forms to pass through embryonal forms because 

 their ancestors have once existed in this condition. To take 

 a special case, suppose in the course of generations a species 

 has increased its length of life gradually from one, two, three 

 years to eighty years. The last animal would have had 

 ancestors that lived for one year, two years, three years, etc., 

 up to eighty years. But who would claim that because the 

 final eighty-year species must pass necessarily through one, 



