REMARKS ON REGENERATION 341 



observed that the injured Pycnogonides continue to molt. 

 I expect to resume these experiments and to fill out the gaps 

 left in this study. 



II. ON THE THEORY OF REGENERATION 



1. Systematists have found it difficult to place the Panto- 

 pods in the natural system upon the basis of their morpho- 

 logical and developmental characteristics. It might be 

 thought that under such conditions the consideration of the 

 physiological behavior of the animals might offer advantages. 

 On the basis of our observations on the regeneration of 

 Pantopods it might appear as if the Pantopods were closely 

 related to the Annelids ; but this conclusion would be inac- 

 curate, for, as is well known, a whole group of Annelids, the 

 leeches, do not regenerate body segments which have been 

 lost, even though transverse pieces cut from the leech may 

 remain alive for more than a year. One would therefore 

 have to reason that the Pantopods are more closely related 

 to the Chsetopods than the Hirudinese, which would be 

 absurd. 



2. One frequently encounters the statement that the 

 capacity for regeneration in animals decreases the higher 



-animals stand in the natural system. This idea has been 

 stated in a very definite form by Nussbaum: "The capacity 

 of regeneration of organisms is proportional to their sys- 

 tematic position, as determined by their characteristics, and 

 decreases from below upward." 1 This generalization goes 

 too far, as can be seen from the facts mentioned above. 

 Usually we find in every large group in the animal kingdom 

 certain species with a greater, and others with a smaller 

 power of regeneration. The salamander regenerates an 

 amputated tail, inclusive of the spinal column and spinal 

 cord, and this power of regeneration is almost as great as 



i NUSSBAUM, Sitzungsberichte der N iederrheinischen Gesellschaftfiir Natur-u. 

 Heilkunde. Bonn, November 5, 1894. 



