342 STUDIES IN GENERAL PHYSIOLOGY 



that observed among the Chaetopods or Pantopods. On the 

 other hand, the leech is not much more capable of regenera- 

 tion after an injury to its body than the human being; both 

 can only cover the amputated stump with skin. If one wishes 

 to utilize the power of regeneration of animals for phylo- 

 genetic purposes, this can be done only for members belong- 

 ing to one and the same morphological group. According 

 to Sachs, only "the forms of the same group may be con- 

 sidered related to each other ; they have nothing in common 

 phylogenetically with the members of another group ; every 

 morphological group is, so to speak, a plant kingdom in 

 itself." 1 



But whether even within the same phylogenetic group, 

 in the sense in which Sachs uses the term, the power of 

 regeneration of a species is a simple function of its position 

 in the group can at present, from lack of facts, not be decided. 

 My experiments on the functions of the brain in worms 

 showed that no parallelism exists between these functions 

 and the systematic position of each species. Much less does 

 such a parallelism exist in regard to the tropisms which can 

 be altered comparatively easily through external conditions. 

 But though it is not correct to say that the power of regener- 

 ation decreases the higher the animal stands in the system, 

 it is perhaps true, that the number of species capable of 

 complete regeneration is relatively greater in the groups of 

 the Ccelenterates and worms than in the groups of Arthro- 

 pods and vertebrates. 



3. In general, it will also be found correct that the power 

 of regeneration is greater in the embryo than in the adult 

 animal. The young larva of the frog regenerates an ampu- 

 tated leg, while this is not possible in the adult animal. 

 Those who assume that the power of regeneration is the 

 greater the lower the position of the animal in the natural 



1 J. VON SACHS, Flora, 1894, p. 219. 



