GENETICS: K. S. LASHLEY 
301 
Twenty-five variates from a single clone were selected for seven or 
more tentacles, and 25 for six or less, the mean of the clone lying between 
six and seven. Selection was continued for six or more generations. At 
the end of this time records were kept of all buds produced by the last 
selected generation. Those produced by parents from the series selected 
for few tentacles were found to have somewhat fewer tentacles than 
those from parents of the other series, but the difference appeared only 
in the first six buds and did not persist in the later buds produced by 
the same parents. The average number of tentacles of the first six 
and of later buds produced by the last selected generation is shown in 
the following table. 
Buds of the Last Selected Generation 
AVERAGE OF ALL 
FIRST SIX 
LATER BUDS 
Selected for many tentacles 
6.695 ± 0.023 
6.677 =t 0.029 
6.712 ^ 0.030 
Selected for few tentacles 
6.605 ± 0.026 
6.460 ± 0.034 
6.782 =±= 0.037 
Difference 
0.095 ± 0.035 
0.217 ± 0.044 
-0.070 ± 0.047 
Continued selection at first seemed to have produced a change in the 
hereditary character of the two groups but this did not persist even 
through a single generation. Complete regression appeared as soon as 
the polyps reached maturity. 
An almost identical result was obtained in an earlier experiment on 
the effects of injury. Polyps which had regenerated the mouth and 
tentacles showed a marked reduction in the number of tentacles of the 
buds which they produced immediately after regeneration, but the av- 
erage number of tentacles of successive buds formed after regeneration 
increased until at the end of two weeks, when four to eight buds had 
been produced, the polyps had returned to the normal condition of the 
clone from which they were derived. 
The similarity of these results makes it certain that the only effect of 
selection was a temporary change in the vigor of the selected polyps 
(the selection of individuals with few tentacles involving the selection of 
weaker polyps) and that there is no cumulative inheritance of varia- 
tions in the number of tentacles within the clone. Races of Hydra 
differing in their hereditary number of tentacles exist but individual 
variations do not involve changes in the hereditary constitution of such 
races. 
Some evidence that the same conclusions apply to the inheritance of 
size was obtained, but the relation of variations in size to environmental 
changes has not been investigated thoroughly. 
