The Theory of Evolution 57 
In regard to the larval forms of other groups we find the 
same relations, as, for example, inthe 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. 
