MORPHOLOGY AND PHYSIOLOGY OF GENUS URONYCHIA 385 



under the same conditions and differing only in the possession 

 of two microniiclei, both pieces regularly did regenerate and 

 divide. 



It is not easy to cut Uronychia in such a way that either piece 

 will be free from a part of the macronucleus. In fact, it would 

 be impossible to be sure that some of the macronucleus was not 

 included, for there is so much variation in that structure. These 

 experiments do not offer any evidence of its function. 



The fact that various monsters have been produced by in- 

 juring the cells in the region of the micronucleus indicates that 

 it regulates the growth processes. In those experiments in which 

 the micronucleus was destroyed during the division process 

 (cf. table 12) the process of regeneration of new cirri did not stop 

 at the usual time and monsters resulted. Even in the regenera- 

 tion of amicronucleate pieces resulting from cuts not made dur- 

 ing division, it was noted occasionally that the cirri continued 

 growth throughout the life of the cell. Usually the cell died 

 from starvation before striking abnormalities were produced. 

 This function of the micronucleus might be compared with the 

 regulating action of the endocrine organs in the metazoa. 



In summarizing his work on Uronychia transfuga. Calkins 

 wrote as follows: "The results might be interpreted by the as- 

 sumption of a specific substance, possibly enzymatic in nature 

 which accumulates with the age of the cell until a condition 

 analogous to saturation is reached. With the formation of the 

 new cell organs this substance, it may be further assumed, is 

 exhausted and regeneration is impossible save with the full com- 

 plement of cell organs." These experiments seem to bear out 

 such conclusions. A comparison of these results with those 

 obtained from the experiments on U. transfuga seems to show 

 that this substance accumulates in the protoplasm of the cell 

 at an earlier period in the American species. For instance, 

 Calkins found that regeneration of fragments without a micronu- 

 cleus was seldom completed if the cutting was done before the 

 animal had begun its division. In U. setigera, however, after 

 five or six hours had elapsed since division, amicronucleate pieces 

 almost always regenerated the lost parts and assumed a more 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 36, NO. 3 



