52 A. FRANKLIN SHULL 



GENERAL ACCOUNT OF THE EXPERIMENTS 



The diagram in figure 1, with the following description, will 

 make clear the nature of the whole series of experiments. The 

 parthenogenetic lines used were derived originally from rotifers 

 collected in Grantwood, New Jersey, one in March, the other 

 in May, 1911. These lines were designated A and B, respec- 

 tively, in a foniier paper. Females of line A were inbred with 

 males of the same line, and from one of the fertilized eggs a new 

 line was started; this line is designated C. Females of line A 

 were mated with males of line B, and from one of the fertilized 

 eggs a second parthenogenetic line was started; this line is desig- 

 nated D in the diagram. 



Lines C and D were each inbred (C X C and D X D), and 

 reciprocal crosses between them were obtained {C X D and 

 D X C). In these crosses the female parent is named first. The 

 inbred eggs were discarded after determining how many of them 

 would hatch, but from each of the reciprocal crosses a new par- 

 thenogenetic line was derived. Throughout the diagram, a batch 

 of eggs and the parthenogenetic line or lines derived from one 

 or more of them are regarded as a unit, since all individuals 

 between one fertilization and the next are believed to have the 

 same genotypic constitution, and are included in one rectangle 

 of the diagram. 



The two reciprocal crosses (C X D and Z) X C) were each 

 inbred [(C X D) X iC X D) and {D X C) X {D X C)], and 

 reciprocal crosses [{C X D) x {D X C) and {D X C) X {C X D)] 

 also obtained. Three of these were discarded after determin- 

 ing the viability of the fertilized eggs. The fourth, the inbred 

 (C X D) X {C X D) was continued as two parthenogenetic lines, 

 one started from a family of eggs showing low viability, the 

 other from a family showing high viability of the eggs. 



Each of these two lines was inbred, and from the fertilized 

 eggs two parthenogenetic lines started. The line from the low 

 viability line was started from an egg in a family that hatched 

 few of its eggs (Li) ; that from the high viability line was derived 

 from an egg in a highly viable family (Hi). These two lines 

 were again inbred. Fertilized eggs were again selected from 



