330 SEEGIUS MORGULIS 



studying different lots of animals as representatives of the differ- 

 ent stages of regenerations, it must be granted that the continuity 

 of the process may be traced with a high degree of probability. 

 In this investigation the stages of regeneration are distinguished 

 by the number of days elapsed since the operation, and while not 

 all individuals are in exactly the same conditions, the irregularities 

 are probably of not much significance, since large numbers of 

 worms have been used for each determination. 



Another serious objection is that the regenerated tissue is not 

 studied alone, but in conjunction with the old tissue. This, of 

 course, makes it impossible to decide whether the change in the 

 water content is localized or not. Fortunately, later examinations 

 of the quantity of water in the regenerating tails of salamanders, 

 to which I shall refer again at the close of the paper, show beyond 

 a doubt that the increase of the water content is here confined 

 to the regenerating tissue. Tf the results of this investigation on 

 salamanders may be relied upon in interpreting phenomena ob- 

 served in regenerating Podarke, the modification of their per 

 cent of water may likewise be considered as localized in the regen- 

 erating tissue. However, as will be seen later, the conclusions 

 from the study of Podarke are not affected by this complication. 



Still another objection to this investigation arises from the 

 fact that, owing to the smallness of the animal experimented on, 

 masses of worms, rather than individual worms were studied; 

 in other words, the results are based entirely upon averages. This 

 objection is very potent, and in interpreting the facts I have 

 kept it clearly in mind. The method of averages is certainly open 

 to many serious criticisms, but the deficiencies of the method may 

 be compensated to a certain extent by increasing the number of 

 experiments, for this reason, as will be seen in what follows, 

 stress is laid only upon phenomena which are fairly constant 

 in all experiments. 



Besides those already recounted, there are several other un- 

 avoidable sources of error, as might be expected in work which 

 requires such delicate technique. Every effort, however, has been 

 exercised to minimize the possibility of error ; but in contemplating 

 the results it will be found necessary to make allowance for 

 disturbing factors which could not be avoided. 



