LIMITS OF HEREDITARY CONTROL 865 
secondary we have here some four or five elemental units. In the 
neighborhood of the bands these gradually fuse together, and in 
the region immediately adjacent to the ninth band are usually 
typified by two pieces, one, a regular trapezoid in shape, forming 
the anterior part, and the other, triangular in outline, abutting 
against this posteriorly. In the true bands these two pieces 
fuse to form the characteristic secondary scute. 
A great deal of interesting data might be given concerning the 
much more primitive condition of the integumentary elements 
as seen on the ventral side of the animal, but it must be sufficient 
merely to suggest one or two of their more salient features. On 
the belly the horny structures only are present, and these are 
associated with a group of five or six hairs, oreven more. On the 
legs some few of the larger horny elements, especially those which 
have a tendency to be arranged into definite rows, are underlaid 
with true bony plates. Evidently the hair group is the most 
primitive element of the complex, and in connection with these 
elements have grown up the scutes and plates. 
MERISTIC VARIATION OF THE ELEMENTS OF THE NINE BANDS OF 
ARMOR 
A. Variation in the banded region as a whole 
It is our purpose to present in this section only so much of the 
results of our studies of the variability of the species as appears 
to be prerequisite for an understanding of the phenomenon of 
fraternal correlation. A concise tabulation of the distribution of 
the variates and a determination of the principal variation con- 
stants should serve the purpose in view as well as would a more 
detailed account. 
That the characters dealt with show a high degree of variability 
is obvious if one examine the array exhibited in table 2. The 
number of scutes in the banded region vary all the way from 517 
to 625, a range of nearly 20 per cent. In connection with our 
studies on fraternal correlation it will be of value to bear in mind 
this high species range of variability. In table 2 is presented the 
array of individuals investigated, comprising 508 adults and shells, 
