NOTES ON REGULATION IN STYLARIA LACUSTRIS. 177 



the fission zone might be traceable to other causes than the in- 

 fluence of the regenerating region. The results here given are, 

 however, relied upon in the belief that the early disappearance of 

 the zone of fission (in all cases in about two or three days) suffi- 

 ciently indicated that it was due to the influence of the regenerat- 

 ing region. There is also the evidence of the cases to be 

 mentioned later in, which the zone of fission did not disappear 

 subsequent to a cut behind the zone of fission. 



An effect is produced the converse of what has just been de- 

 scribed when an animal is severed in front of and near to a well- 

 advanced zone of fission. In such a case its development exerts 

 a retarding influence on the regenerating region. A small piece 

 in front of such a zone of fission is soon separated, after under- 

 going little or no regeneration. 



4. Effects of section behind a recently formed zone of fission. 



Section behind a recently established zone of fission does not 

 ordinarily seem to exert an inhibitive influence. In only one 

 such case observed was the zone redifferentiated. No change is 

 produced, unless it be a retardation of the development of the 

 zone of fission. Two considerations seem to have weight in ex- 

 plaining the difference between this and the case in which the 

 cut is anterior to the fission plane. First, the regeneration of the 

 anal segment is a process requiring the withdrawal of less material 

 from the old parts than the regeneration of an anterior end, and 

 hence is calculated to interfere less with the development of the 

 zone of physiological regeneration. Second, the establishment 

 of a regenerating region behind the zone of fission does not 

 materially change the conditions already existing in that region, 

 since in this case a regenerating region posterior to the fission 

 plane is substituted for the previously existing proliferating re- 

 gion in front of the anal segment. 



Galloway ('99) has noted in respect to Dcro vaga that cutting 

 behind the fission zone tends to disorganize its growth and the 

 posterior piece soon drops off. 



As a parallel to the results of the preceding experiments upon 

 Stvlaria it may be mentioned that Dr. Child has informed me 

 that he has found a similar disappearance of the fission plane in 

 the Rhabdoccele Stenostoma. under the influence of a regenerating 



D O 



