« 
60 Variation in Chilomonas 
graduate with some curve, which, while still remaining symmetrical about the 
mean, has a sharper peak than does the normal curve. The breadth distribution 
for Series A is sensibly mesokurtic, with a value of 77 = •1332 and a probable error 
of + •2331. The same is true for the length distribution of Series B, though in 
this case the value of 77 is somewhat larger. The breadths in Series B give a 
value for 77 of + •8834 with a probable error of + ^2498 ; the distribution is 
significantly platykui'tic. 
Putting all the results together we conclude that the individuals of Series A 
vary symmetrically about their type condition, while those of Series B exhibit 
skew variation. For the character length this skevvness is slight and taken by 
itself could not be considered significant, but considering that the length and 
breadth distributions of this series (B) exhibit deviations from normality in the 
same direction with respect to all constants we may safely conclude, I think, 
that we are dealing with a case of real skewness. This conclusion is of interest 
when it is recalled that Series A represents the extreme of unfavourable 
environmental conditions, and Series B the optimum environment. This point 
will be more fully discussed farther on in the paper. 
From the values of /Cj and k.2, j3i and /3.2, it is clear that the length distribution 
of Series A calls for a curve of Type II ; the breadth distribution of Series A for 
a normal curve ; while both length and breadth distributions of Series B demand 
curves of Type IV. 
The frequency distributions and their fitted curves are shown graphically in 
Figures 2 and 3. The equations to the curves are : 
Series A, Length. 
/ ^2 \ 4-4084 
Typell 2/ = 28-6889 (l-^j^) 
Origin at mode = 22'555 mikrons. 
Series A, Breadth. 
Normal. ?/ = 37-9978 e -'^^i^' 
Origin at mode = 9^479 mikrons. 
Series B, Length. 
Type IV. 2/- 4^7077 (cos ^)*5-7"ie™^'' 
ic=15^9676 tan^ 
Origin at 19^973 mikrons. 
Series B, Breadth. 
Type IV. y = 14-5990 (cos ^ys-3703 e4-95949 
x= 7-7502 tan 0 
Origin at 9-375 mikrons. 
Considering the small number of observations these curves give very good 
graduations. The skewness of the Series B distributions is very apparent in these 
