610 
GENETICS: R. J. STOCKING 
tion to this question: Can we by continued selection of normal indi- 
viduals on the one hand, of abnormal individuals on the other, break 
our single stock into two or more, differing in hereditary constitution? 
The results of this study are as follows : 
1. The diversities in abnormality occurring within a single line of 
descent (derived from a single excoiijugant) are in some lines not heredi- 
tary, so far as can be determined by long continued selection. In a 
very large proportion of the races in which the abnormals were regularly 
discarded and only normals retained to carry on the race, the abnormal 
character persistently reappeared, the selected normals producing abnor- 
mal progeny. In all the abnormal races there is a wide variation in 
degree of abnormality of the individual, from those perfectly normal 
to the monsters so deformed that they would never be recognized as 
Parameciaif their history were not known. Yet, as stated above, in 
most cases the progeny of all these variations were alike, the daughter 
cells of normal individuals being often just as abnormal, or even more 
so, than the daughter cells of monsters. This of course agrees with 
the conditions found in most of the studies on inheritance in 'pure lines' 
or clones; the diversities within the lines are not inherited. 
2. But in other lines, diversities within the line showed themselves 
to be heritable, so that selection gave very different results from those 
usually obtained in pure line work. By selection, single lines, derived 
by fission from a single parent, were divided into two or more races 
differing hereditarily. This was successfully accomplished in twenty- 
five races; from each of these were isolated two lines, one quite normal, 
the other continually producing abnormalities, — the two cultivated side 
by side. 
Calkins and Gregory^ have in some cases obtained four diverse races 
from the four primary daughter cells, or ' quadrants' of an exconjugant 
— these being the four individuals that receive the four macronuclei 
produced before fission occurs. It is to be noted that our selection 
resulting in the isolation of lines differing hereditarily in abnormality 
often has been brought about much later in the series of generations, so 
that the differentiation has often occurred within the compass of a single 
'quadrant,' or indeed within a much narrower fraction of the descent. 
In several cases, differentiation through selection did not begin till after 
several weeks had passed, with production of a great number of gen- 
erations. Thus the results of selection in the present case cannot be 
interpreted as due to a primary difference in the four original macronuclei 
produced during conjugation. Selection is effective when begun with 
progeny of a single individual that has appeared many generations after 
conjugation. 
