444 RUTH J. STOCKING 



VII. SIBIMARY AND DISCUSSION OF RESULTS 



Among the progeny of a large proportion (from 36 to 81 per 

 cent in the different experiments) of exconjugants of Paramecium 

 caudatum, abnormahties appear frequently and constantly. 



These abnormalities show themselves to be hereditary in the 

 following respects: 



1. Lines derived from different exconjugants differ in respect 

 to them: some lines show no abnormalities; others show a small 

 proportion of abnormal individuals; others large proportions up 

 to cases in which abnormality is almost or quite universal. 

 The tendency to abnormality is transmitted in fission; definite 

 proportions of abnormality being characteristic of particular 

 lines. In one case there was inheritance of a specific type of 

 abnormality carried through 303 generations (Race C). 



2. The diversities in abnormality occurring within a single 

 line of descent (derived from a single exconjugant) are in some 

 lines not hereditary, so far as can be determined by long con- 

 tinued selection. In a very large proportion of the races in 

 which the abnormals were regularly discarded and only nor- 

 mals retained to carry on the race, the abnormal character per- 

 sistently reappeared, the selected normals producing abnormal 

 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 paramecia if 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 inlieritance in 'pure lines' or clones: 

 the diversities within the lines are not inlierited. 



3. But in other lines diversities within the line showed them- 

 selves 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 success- 



