474 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



net-work of capillary blood-vessels. Eventually each vesi- 

 cle, increasing in size, gave off at its free end three or four 

 short, blunt branchlets; but, even when fully developed, 

 these secondary gills did not equal in length the diameter of 

 the animal's head, so that, although agreeing in number with 

 the primary feather-like gills, they differed from them in 

 every other particular. When they had attained a certain 

 size, the larva resumed its active habits, to which the small 

 outstanding 2,'ills offered no hindrance." 



There was, however, a great difference between the two 

 survivors in the length of time taken to develop the adult 

 characters. The less-advanced larva did not begin to cast 

 its skin or lose the (secondary) swimming membrane of its 

 tail till the fourteenth week of its aquatic life, and not until 

 the sixteenth week were the gills lost ; while in the more 

 matured larva, at the end of the second week of its extra- 

 uterine existence the gills had been dropped, and the animal 

 left the water to lead a terrestrial life. 



It is noticeable that, notwithstanding the great disparity 

 in the number of young born to the two species of Salaman- 

 ders, the adults are about equally numerous in the regions 

 in which they respectively occur, and we have thus a strik- 

 ing exemplification of the perils which the unprotected and 

 immature young, and still more the eggs of animals, are sub- 

 jected to. But even those animals in which the young are 

 born i in maturely have a great advantage over the oviparous 

 species, and in the last, consequently, eggs are developed in 

 vast numbers to insure the perpetuation of the species; as 

 witness, for example, the codfish, which develops eight to ten 

 millions of eggs in its ovary. Nature rarely fails to adjust 

 the conditions to the surroundings. 



For further details and speculations as to how the differ- 

 ences between the two species of Salamanders originated, we 

 must refer to the original article in the ZeitscJirift filr wis* 

 senschaftliehe Zoologie, vol. xxix., and the Nineteenth Centu- 

 ry for March, 1878. 



Natural Selection Exhibited in the Development of Amolystoma 



Larva}. 



Collateral with the experiments of Miss von Chauvin may 

 be placed the observations of Mr. Samuel F. Clarke, a fellow 



