286 



EVOLUTION AND ANIMAL LIFE 



or other nuclear stuff that is the actual carrier of the paternal 

 heredity are of course actually wanting. 



Another phenomenon or group of phenomena, also of much 

 special interest and suggestiveness to students of develop- 

 ment, to which the experimental method has been successfully 

 applied, is that known as " regeneration. " The familiar repro- 

 duction or growth of 

 new plants from cut- 

 tings or buds is par- 

 alleled in the animal 

 world by numerous 

 similar cases less fa- 

 miliar but neverthe- 

 less long known by 

 naturalists. In 1740, 

 Abbe Trembley made 

 a number of curious 

 experiments with Hy- 

 dra, whose publication 

 in 1744 w r as the begin- 

 ning of our knowledge 

 of the phenomena of 

 regeneration in ani- 

 mals. If Hydra, the 

 common little brown 

 or green fresh-water 

 polyp, be cut up into 

 many pieces, each of 

 these pieces has the 

 power to grow into a 

 new complete Hydra 



body (Fig. 164). We know now that numerous other animals 

 have also this radical capacity for regeneration. Certain pro- 

 tozoans, hydroids, planarian worms, starfishes, etc., can re- 

 generate as freely or nearly so as Hydra (Figs. 165-172). And 

 many other animals representing almost all the great groups of 

 the animal kingdom possess in some degree, at least, the power 

 of regeneration. Some can regenerate only lost or cut append- 

 ages, others even less fundamental parts of the body; some 

 can regenerate only in their immature stages ; others only in 

 the earliest embryonic stages. But regeneration and "regula- 



FIG. 169. Regeneration of the tail and limbs of 

 the lizards, Lacerta agilis and Triton custatus : 

 A, Lacerta, new tail arising at place where old tail 

 was broken partly off; B, three-tailed form, two 

 tails having a common covering, all these parts 

 being regenerated after old tail was cut off; C, 

 Triton, additional leg produced by wounding femur; 

 D, double foot produced by tying thread over re- 

 generating stump; E, F, G, regenerated feet of 

 Triton after various mutilations. (After Tarnier. ) 



