THE PHYSIOLOGY OP REGENERATION 331 



With this exordium, I now reiterate the problem of which this 

 paper is a partial solution. The curves of formative and regener- 

 ative growth being strikingly similar the question arises whether 

 both processes are due to similar causes, and especially whether 

 the different stages of regeneration, characterized by different 

 intensities of regenerative energy, are accompanied by correspond- 

 ing changes in the water content of the tissues, as has been demon- 

 strated to be the case in ordinary growth. 



EXPERIMENTS ON PODARKE OBSCURA 



All the experiments described below were conducted in the 

 following manner. Several hundred specimens of Podarke 

 obscura, collected in the eel-pond at Woods Hole, were operated 

 upon immediately or very soon after they had been brought into 

 the laboratory. The worms were always cut in two near the middle 

 of the body and the anterior halves were placed in a single large 

 dish half filled with sea-water. In some experiments, the worms 

 were kept in pure sea-water, the water being frequently changed; 

 in others they were also provided with food, consisting of the 

 vegetation of the eel-pond. The outcome of these two sets of 

 experiments, with and without food, though differing in some 

 minor matters, conform to each other in the main. As soon as all 

 worms had been operated on, a sample, taken at random and con- 

 taining forty to fifty specimens, was examined for its water con- 

 tent. This sample served as control for the experiments, the result 

 being compared with the results of similar determinations made 

 for worais of the same series, but kept for two to forty days after 

 operation before being tested for water content. 



First series 



Experiment A. This experiment (compare table 1 and fig. 5) 

 was started on July 7, and 40 worms, taken at random out of the 

 400 operated upon, were examined on that day. These 40 live 

 specimens, previously dried on filter paper to remove all traces 

 of water from the outside, weighed 72.9 mgrms., or on an average 

 1.823 mgrm. The worms were then dessicated over sulphuric 



