326 THE POPULAR SCIENCE MONTHLY 



case of my tadpoles, it seemed that the completion of development was due to 

 my imprudently feeding them in spring of 1891 on the very substantial flesh of 

 their congeners; and in the course of some three weeks at most the limbs were 

 evolved, the long tail disappeared gradually, the very color and appearance of 

 the skin underwent considerable change, and my superannuated tadpoles became 

 toads at last. 



Modifications of this sort are shown in the experiments of Kammer. 2 * 

 Salamandra atra acquires yellowish white spots through higher tem- 

 perature and moisture. Low temperature and dry conditions make 

 Salamandra maculosa more black in color with a diminution of the 

 yellow spots. 



The amphibians show good powers of regeneration, but their faculty 

 in this direction is neither more nor less than is warranted by their 

 position in the phylogenetic scale. This is well indicated by Przibram. 30 

 In their younger and lower types they belong in the fourth class of 

 animals, or those which can regenerate not only the tail, but also limbs, 

 sense organs and other portions of the body as long as the central 

 nervous system is not removed. More adult and higher types lose some 

 of this power and then may regenerate the tail only or only certain 

 tissues. 



The general conclusion from all these experiments on amphibians 

 involving artificially induced changes in the condition of temperature, 

 light, gravity, salt, electricity, oxygen and food is that when we arrive 

 as high in the phylogenetic scale as the amphibians very little can be 

 done to permanently modify the predetermined forces of the germ- 

 plasm. As among fishes the most striking permanent changes are con- 

 cerned with the pigmentation. 



Reptiles 



In powers of regeneration the reptiles show their higher phylo- 

 genetic rank. The lizard can regenerate the tail, but not the limbs. It 

 is interesting that the new tail is not composed of bones, but is a carti- 

 laginous tube attached to the half of the broken seventh caudal verte- 

 bra. 31 Snakes and turtles will not regenerate their tails. 



Modification experiments, other than those concerning regeneration,, 

 are not numerous or suggestive. I find only reference to the well-known 

 pigmental response of the chameleon. 



Birds 

 As we ascend the scale we not only find that modification experi- 

 ments are less striking in character, but also find fewer experiments 

 recorded. Noteworthy modifications of birds are almost entirely con- 



29 Arch, fur Entwickelungs Mechanik, XVII., pp. 1G5-264. 



30 " Regeneration," Leipzig, 1909, Taf. XVI. 

 81 Morgan, " Regeneration," pp. 6, 198. 



