The Theory of Evolution 57 



In regard to the larval forms of other groups we find the 

 same relations, as, for example, in the amphibians. The young 

 of salamanders, toads, and frogs leave the egg not in the 

 completed form, but as small tadpoles adapted to life in the 

 water. A certain resemblance to fish cannot be denied. 

 They possess a broad tail, gills (rich in blood vessels) on 

 each side of the neck, and limbs are absent for a long time. 

 These are characters similar to those of fish, but a more care- 

 ful anatomical examination destroys the apparent resemblance. 

 The superficial resemblances are due to adaptation to the 

 same external conditions. 



Fleischmann ridicules the idea that the young chick 

 resembles at any stage an adult, ancestral animal ; the pres- 

 ence of an open digestive tract shows how absurd such an 

 idea is. The obvious contradiction is explained away by 

 embryologists, by supposing that the ancestral adult stages 

 have been crowded together in order to shorten the period of 

 development ; and that, in addition, larval characters and pro- 

 visional organs have appeared in the embryo itself, which 

 confuse and crowd out the ancestral stages. 



In regard to the presence of gill-slits in the embryo of 

 the higher vertebrates, in the chick, and in man, for example, 

 Fleischmann says : " I cannot see how it can be shown by 

 exact proof that the gill-slits of the embryos of the higher 

 vertebrates that remain small and finally disappear could 

 once have had the power of growing into functional slits." 

 With this trite comment the subject is dismissed. 



On the whole, Fleischmann's attack cannot be regarded as 

 having seriously weakened the theory of evolution. He has 

 done, nevertheless, good service in recalling the fact that, 

 however probable the theory may appear, the evidence is 

 indirect and exact proof is still wanting. Moreover, as I 

 shall attempt to point out in the next chapter, we are far 

 from having arrived at a satisfactory idea of how the process 

 has really taken place. 



