LIMITS OF HEREDITARY CONTROL 915 
These are so closely associated and so definitely inter-related that 
a study of one element furnishes an index of the variability of all. 
For convenience, the external element, the scute, is chosen for 
statistical study. When the term ‘scute’ is used the whole com- 
plex is to be understood. 
4. A statistical study of the species variation in the nine bands 
reveals the facts that we are dealing with a highly variable char- 
acter which fluctuates according tothelawsof chance. The mean, 
mode and median practically coincide, and the observed and the 
theoretical variation curves are very similar. 
5. Males are decidedly more variable than females with respect 
to the characters studied. 
6. The variability of the bands taken separately is proportion- 
ately greater than that of the banded region as a whole. In each 
band, however, the variation in the numbers of scutes appears to 
take place according to the laws of chance. 
7. The twenty sets of normal foetuses furnish an ideal array 
for the study of fraternal correlation. Taking each set as a fra- 
ternity, and dealing with the total number of scutes in the banded 
region, a correlation coefficient of .9348 is obtained. This is taken 
‘as an index. of the strength of hereditary control with respect to 
the character in question. The only correlation constants at all 
comparable with this are those derived from a study of the anti- 
metrically paired organs of the same individual. This fact con- 
firms the idea of the polyembryonic origin of the quadruplets, and 
shows that, morphologically, we are dealing with four parts of one 
individual. 
8. The correlation coefficients determined for the individual 
bands are comparatively so low that the conclusion is reached that 
the process of scute alignment is largely mechanically determined 
and hence beyond the limits of hereditary control. 
9. A study of the atypical variation in the banded region shows 
that there are several types of scute ‘abnormality,’ double scutes, 
split scutes and the three-hair type of scutes; and also several 
types of band ‘abnormality,’ fusions, splittings and additions. 
All of these conditions are comparatively rare and highly diver- 
sified in detailed expression. 
