138 Dynamic Theory. 



young Salamanders are taken out of the mother at a certain time and 

 placed in the water, they will breathe by their gills, their development 

 will continue and they will finally become land Salamanders. Their de- 

 velopment in the matrix of the female is much more rapid than when 

 they are thus taken out, a fact recalling the compression, within this 

 short space of time, of the adult lives of the ancestral forms, which takes 

 place more or less distinctly in all embryonic development. (Wilson's 

 Evolution, 244.) 



The history of this Salamander is, no doubt, in the same direction as 

 that of the Axolotl, and indicates that its modification has been caused 

 by an increasing habit of living without the water. It has either 

 climbed the mountains, leaving the water behind it, or the mountains, 

 in being elevated in ancient times, carried it upward and gradually the 

 water disappeared, and the amphibian was modified to suit. The fact 

 that the embryonic gills of this animal are real and capable of perform- 

 ing functions which, nevertheless, in a state of nature they are never 

 called upon to perform, is exceedingly curious and instructive. It 

 points conclusively to a time in the past, not very remote, relatively, in 

 which the young Salamander was born before he parted with his gills, 

 and habitually used them in aquatic respiration. And it illustrates the 

 point so much insisted upon by evolution, that the development of every 

 individual involves the imitation of every successive stage in his ances- 

 tral line, all the stages but the present being compressed into the short 

 period of his antenatal life. 



The fact is, that every vital process is a matter of habit. Every 

 form is an outgrowth of its predecessor, and, consequently, cannot ap- 

 pear till its predecessor has appeared. It is the endless repetition of 

 this succession of forms that has given it the facility that constitutes 

 habit. The older stages have been repeated of tener than the later ones, 

 consequently they are passed over more rapidty. Every generation 

 compresses into the last moments of its prenatal life the essence of the 

 modifications that took place in the preceding generation. The course 

 of this prenatal development is under the influence of the environment, 

 but that influence has a much less modifying effect upon the earlier 

 than upon the later stages, because the earlier are more firmly fixed in 

 the line of habit. It is on this account that the larval stages of the in- 

 vertebrates and lower vertebrates, which answer to the later prenatal 

 stages of the higher vertebrates, are, to so great an extent, subject to the 

 influences of the environment heat and cold, moisture and dessication, 

 quality and quantity of food, &c. 



The fact that such larval forms as the Axolotl, are able to reproduce, 

 shows how exactly the later of its ancestors, in their adult form, are 

 imitated, in its now larval form, so exactly that all the essential vital 

 functions of the ancient adult are copied by this infant. 



