346 GENERAL ZOOLOGY 



also probable that in the ontogeny of any animal there is 

 wide discrepancy as regards the proportion of time between 

 various embryological stages and comparable stages of the 

 ancestors when in similar condition. Despite such imper- 

 fections in the ontogenic narrative, the development of 

 animals, when taken with other evidence, gives valuable 

 support to the theory of evolution. 



To quote Thomson and Geddes: "It must be admitted 

 that the recapitulation doctrine has been often stated in 

 somewhat crude and exaggerated form, so that many saving 

 clauses are necessary. The human embryo is never like a 

 little fish or a little reptile; the resemblance is between 

 embryonic stages. The recapitulation is general, not exact; 

 there is often abbreviation and a masking of the old by 

 the new. . .. . It must also be frankly admitted that 

 we are apt to get into a vicious circle in arguing about 

 recapitulation. We infer the pedigree from the develop- 

 ment, and then say that the development recapitulates the 

 pedigree. . . . But when all is said, there remains good 

 reason for keeping firm hold of this idea that 'ontogeny, 

 or the development of the individual, is a shortened 

 recapitulation of phylogeny, or the evolution of the race." 



Morphology and Classification. If animals are classified 

 on a structural basis without regard to evolutionary theories, 

 they arrange themselves so that those which are genetically 

 related come in the same group and a sequence is established 

 which has evolutionary significance. Studies in classifi- 

 cation and cataloguing first suggested evolution to Lamarck. 

 At the present time systematic zoologists use all the evi- 

 dences of evolution in attempting to establish more 

 " natural" systems. Modern classification is founded on 

 genetic relationship as judged by ontogeny, phylogeny, 

 morphology, and physiology. A correct system of classi- 

 fication is also a genealogical tree. 



Morphology, of itself, furnishes good evidence for 

 evolution. The presence of useless vestigeal organs (man's 

 appendix, whale's teeth) is hard to explain except as a 



