376 DONNELL BROOKS YOUNG 



longitudinal plane (long;. B). In one case, experiment no. 113, 

 division was completed in both parts. Those with micronuclei 

 regenerated in ten to eighteen hours and later divided. The 

 other two pieces died without regenerating completely. In the 

 other case where a longitudinal cut was made, the micronucleate 

 part divided and regenerated, but the amicronucleate piece 

 instead of dividing, doubled on itself and formed a monster 

 which died in about twenty-four hours. In experiment no. 132 

 the cut was oblique (oblique B) and evidently passed in front of 

 the micronuclei, for the anterior part which contained also a 

 small piece from below the division plane divided and both 

 pieces thus formed died without regenerating ; while the posterior 

 part divided and both cells regenerated completely and later 

 divided. In experiment no. 77 the animal was cut much as was 

 the one in experiment no. 84, table 8. The results were the 

 same. The anterior part divided and the anterior cell thus 

 formed lived, regenerated, and later divided while the posterior 

 one died with but slight regeneration. The posterior fragment of 

 this experiment also divided, but the resulting anterior part 

 died, while the posterior part lived and later divided. 



Abnormal regeneration 



Abnormal regeneration — table 10. It sometimes happened 

 that an attempt to cut a cell was not successful and that the in- 

 cision did not separate the two halves. Usually in such cases 

 the wound healed in a few hours and the animal was normal. 

 Individual no. 114 was in an early stage of division when it was 

 injured while attempting to cut it. In this case the plane of 

 the cut was transverse in the center of the body. Instead of 

 dividing normally, the growth of the precocious cirri became 

 abnormal and the cut surfaces fused together so that a monster 

 was formed. This lived for five days and on the fourth had the 

 appearance shown in figure 25. In all probability, in this in- 

 stance the micronucleus was injured by the cut. Two other 

 experiments (nos. 32 and 72) in which abnormal development 

 occurred may be accounted for by this explanation. The first 

 of these was a cell cut twenty-three minutes after division and 



