Eaymond Pearl 
61 
diagrams. They also show clearly to what a marked degree the type of the 
individuals in favourable conditions differs from that of the individuals living 
under unfavourable conditions. The exact amount of this difference is however 
more directly brought out by a comparison of the chief physical constants of the 
distributions, to which we may now turn. 
In Table V are given the means, standard deviations, and coefficients of 
variation, for the characters length, breadth, and index, in the two series. In 
order to facilitate comparison I have also tabulated the absolute differences (with 
their probable errors) between the corresponding constants of the two series. The 
differences are given the plus sign when the Series B constant is the greater and 
the minus sign in the opposite case. 
TABLE V. 
Comparison of Type and Variability of Ghilomonas Living under Favourable and 
Unfavourable Conditions. 
Character 
Series 
Mean 
Standard Deviation 
Coefficient of 
Variation 
Length 
)) 
Breadth 
Index 
)? 
B, Favourable conditions 
A, Unfavourable „ 
Difference 
B, Favourable conditions 
A, Unfavourable ,, 
Difference 
B, Favourable conditions 
A, Unfavourable „ 
Difference 
24-660 ± -1.30 mikrons 
22-55.5+ -125 
+ 2-105±-180 „ 
10-813+ -060 mikrons 
9-479+ -050 „ 
+ 1 -334 ± -078 „ 
44-060+ -203 7 
42-137+ -191 7„ 
+ 1-923+ -279 
2-544+ -092 mikrons 
2 - 629+ -088 „ 
- -085 ±-128 
1-175+ -042 mikrons 
1-0.55+ -035 „ 
+ -120 ±-055 „ 
3- 972+ -143 7„ 
4- 006+ -135 7„ 
- -034+ -197 
10- 318+ -376 
11 - 658 +-397 
- 1 -340 ± -547 
10- 868+ -396 
11 - 132 +-379 
- -264 +-548 
It is seen at once that the differences between the two series in respect 
to type are large. The individuals living under favourable conditions are longer 
and broader both absolutely and in proportion to their length than are those 
living under unfavourable conditions. There can be no doubt that these 
differences between the means are significant in comparison with their probable 
errors. This result shows clearly that even in such a form as Ckilomonas the 
conditions of existence which are favourable to rapid multiplication are also 
favourable to large size of body. Such a relation is, of course, to be expected in 
an organism reproducing sexually, but it is not so obviously necessary a priori 
in an organism reproducing by fission. In fact, it might on general grounds 
be maintained that when the conditions were such as to lead to very rapid 
reproduction by fission, the average size of the individuals would diminish, on 
account of fission taking place before the maximum growth possible had occurred. 
The present data show that such is not the case, however. 
