1908. J 



JENNINGS— HEREDITY IN PROTOZOA. 501 



suppose that the relations we have brought out are Hmited to length 

 alone. Probably other differentiated pure lines could be distin- 

 guished on the basis of other characteristics. 



The only other characteristic on which our data might give results 

 is that of form, as distinguished from size. Are some races broader, 

 some narrower, in proportion to the length? 



We may first examine this question with reference to the two 

 main groups into which most of our lines fall. Is there any general 

 difference in the proportion of breadth to length when we compare 

 the larger races (" caudatiim group ") with the smaller ones {" aurcHa 

 group") ? The experiments whose results are summarized in Table 

 XXV., page 494, give us data for a number of diff'erent lines of both 

 groups, cultivated under the same conditions. We may, therefore, 

 determine the proportion of breadth to length in these. The more 

 accurate way of doing this would be by means of the formula given 

 on page 399. This, however, would involve much computation not 

 made for other purposes ; and we may reach very nearly the same 

 results by simply dividing the mean breadth by the mean length. If 

 the differences between the diff'erent races are not sufficient to show 

 clearly under this treatment, they are doubtful and inconsequential. 

 The following table gives the ratio of mean breadth to mean length 

 in the different lines represented in Table XXV. ; the lines are 

 arranged according to relative size, so as to exhibit any differences 

 between the large and small groups. 



The table shows that the ratio of breadth to length is almost 

 uniformly greater in the small or aurelia group than in 'the larger. 

 The lowest ratios of the aurelia group are, indeed, a little below the 

 highest of the caudatiim group, but the difference between the groups 

 as a whole is unmistakable. The first column of the table is the most 

 satisfactory in this respect, since both sets were killed at the same 

 time. In the second column the difference between the ratios for 

 the two groups is still more decided, but environmental differences 

 may play some part in this case. The average ratio for the cau- 

 datum group is, from the first column 2'j.4y2) V^^ cent. ; from the 

 second 25.679 per cent. For the aurelia group the averages are: 

 first column 30.441 per cent.; second column 31.319 per cent. The 



