384 F. H. Krecker, 



in regional regeneration. However, since many problems had still 

 remained untouched I undertook some investigations on Limnodrilus 

 elaparadianus, a form which had not yet been studied. Although the 

 experiments were begun with Limnodrilus, nevertheless, as the work 

 advanced it was thought best to extend certain phases of it to other 

 forms and so the foUowing pages deal with results obtained from Lim- 

 nodrilus, Tuhifex, Lumbriculus and Lumhricus. For Limnodrilus there 

 were determined the limits of both anterior and posterior regeneration 

 and the minimal size of a piece, at different levels, capable of regene- 

 ration, in addition to which the rate of posterior regeneration during 

 consecutive periods of equal length was considered. This rate was 

 also studied in Lumbriculus in which form the minimal size for extreme 

 posterior levels was likewise found. One of the most interesting phe- 

 nomena observed was a correlation that was found to exist between 

 the intestine and the body wall. It was discovered that posterior 

 regeneration of the body does not occur when the intestine is not in 

 contact with the body wall at the posterior end of the body. These 

 experiments were carried out on Limnodrilus and Tuhifex with similar 

 results in each case. Lumhricus was used for like experiments at the 

 anterior end but in this case a slight amount of regeneration took 

 place. The histological changes which occured in Limnodrilus and 

 Tuhifex upon the removal of the intestine proved of interest and espe- 

 cially with regard to the so-called neoblasts of Randolph. The neo- 

 blasts and the origin of the mesoderm at both the anterior and the 

 posterior ends were also studied in the normal regeneration of Lim- 

 nodrilus and Tuhifex besides which some observations with regard to 

 the mesoderm were made on Lumhricus. 



For the sake of convenience the paper has been divided into two 

 parts, dealing respectively with the internal phenomena and the extere 

 nal phenomena. Under the external phenomena are described thos- 

 experiments and observations for which the Compound microscope 

 was not needed while under the internal phenomena are described the 

 histological results obtained. 



The work was begun at the Suggestion of Prof. C. M. Child of 

 the üniversity of Chicago and many of the experiments described 

 under external phenomena were carried on under his direction. The 

 remainder of the work was done under the direction of Prof. E. Gr. 

 CoNKLiN of Princeton üniversity. I am very greatly indebted to 

 Prof. CoNKLiN for serviceable suggestions and numerous kind favors 

 and I also greatly appreciate the constant kindness and helpful ad- 



