380 LIBBIE H. HYMAN. 



stems bearing larger hydranths, cut at the same time and from 

 the same lot of material. It is perfectly apparent that the more 

 slender pieces regenerate more rapidly, and this was also evi- 

 denced throughout all of my experiments. It is probable that 

 this relation of the rate of regeneration to the diameter of the 

 stem is connected with the age of the stem, but since one does 

 not certainly know that slender stems are younger than stouter 

 ones, the matter must be left open at present. Morgan ('06 6) 

 found that young stems regenerate more rapidly than old ones 

 and that when the hydranths are removed from the top and 

 lateral branches of a stem, the lateral branches regenerate first. 

 At any rate, these facts dispose of the suggestion which has 

 been made that apical pieces regenerate more rapidly than 

 basal pieces because they are of larger diameter and hence contain 

 more protoplasm. As a matter of fact it is the pieces of smaller 

 diameter which regenerate the more rapidly. Further in slender 

 stems there is no difference in diameter along the stem, and yet 

 the apical halves of such stems regenerate hydranths earlier 

 than the basal halves. 



5. Individual Experiments. These experiments were identical 

 with the mass experiments except that each piece was placed 

 in a separate dish and the number of hours required for it to 

 produce an oral hydranth recorded as accurately as possible. 

 The records of the four experiments of this kind which were 

 performed are given in Table V. Experiments 9 and 17 were 

 performed in June at room temperatures; experiments 29 and 

 45 in December at a temperature of 12 C. 2. Pieces were 

 8-12 mm. long except in experiment 29, where they were 5-8 mm, 

 long. There was some mortality in the June experiments but 

 none in December. 



6. Conclusions from Individual Experiments. The results of 

 these experiments lead to the same conclusions as previously 

 stated from mass experiments. Of 122 pairs of pieces in which 

 both pieces regenerated, the apical halves regenerated hydranths 

 first in in cases, or 91 per cent.; the basal halves first in 10 

 cases, or 8 per cent.; and the time of emergence of the hydranth 

 was practically the same in both pieces in one case. Cases 

 where the basal piece preceded in regeneration are indicated by 



