MORPHOLOGY AND PHYSIOLOGY OF GENUS URONYCHIA 369 



Cells md from fifteen to sixty minutes after division 



Sunuuanj of table 3. Twelve individuals of U. setigera were 

 cut into practically equal pieces from fifteen minutes to one 

 hour after division. In one case (no. 134) both pieces died 

 without either completing regeneration. Although neither piece 

 w^as stained, from the position of the cut probably the micronu- 

 cleus was injured. No regeneration of the amicronucleate piece 

 was noted in seven instances (nos. Ill, 118, 112, 36, 42, 134, 

 116). Death of the amicronucleate fragment usually came with- 

 in a few hours of merotomy. In three individuals (nos. 133, 

 135, 130) slight regeneration was seen. All of these were cut in 

 a median transverse plane (transverse B). New posterior cirri 

 appeared as small swellings, but never went further than this 

 in their development. The anterior amicronucleate fragment 

 of one animal (no. 110) cut an hour after division regenerated 

 almost completely. The posterior cirri began to form, but were 

 irregular in their arrangement and never grew to normal size. 

 This fragment died at the end of two days, before the other 

 part had divided. 



Summary of table 4- Eleven individuals were cut into quite 

 unequal pieces from fifteen minutes to one-half hour after divi- 

 sion. Both parts of no. 12 died almost at once. This was due 

 to mechanical injury, for the larger piece was crushed and died 

 before the smaller. One other experiment (no. 128) resulted in 

 the death of both pieces, but before death the larger regenerated 

 completely. The cause of death is not known. Regeneration 

 in the small piece occurred in but one other instance (no. 27), 

 but regeneration was incomplete, the posterior cirri appearing 

 as tiny swellings; the small piece was from the anterior end. 

 One very interesting experiment (no. 46) showed an unusual 

 condition. The first cut failed to injure the body and removed 

 only the last two-thirds of the posterior cirri. A second cut re- 

 moved the anterior end of the cell. Regeneration was complete 

 as far as the anterior membranelles were concerned, but the 

 injured posterior cirri did not develop. At cell division the old, 

 injured cirri were replaced by new ones as usual. This case will 

 be discussed more fully in a later section. 



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



