176 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
dant enough on the average to represent the parental possibilities. Hence the 
second and third classes of (7) are to be combined. Again, it is practically certain 
that among the yellow adults bearing only yellow young are some that are capable 
of bearing yellow and red young, of which the latter do not appear, owing to a single 
offspring only being present. Correcting by the same fractional value of three- 
fourteenths, which is the sole basis for adjustment that it is possible to discover, we 
subtract three-fourteenths of 40, or 8.5, from that figure, and add it to the other 
class, whereupon (7) becomes: 
(12) Yellow adults: yellow young only, 31.5; yellow and red young, 42.5=74 
The contrasted empirical figures differ from the expected numbers by 8.1 per cent. 
Résumé.—When the red color is assumed to be dominant with reference to 
yellow, the analysis of the series displaying the recessive color gives the numerical 
relations of 13:34:27 for the DD, DR, and RR adults, respectively; the test of these 
figures in the independent DD+DR red class shows a departure of observation 
from expectation amounting to 14.4 per cent. If yellow is assumed to be dominant, 
the three genetic classes have the numerical relations of 12 DD:32 DR:77 RR; 
and the difference between expectation and observation proves to be 8.1 per cent. 
The assumption as to the dominance of red is favored by the numerical relations 
of the genetic classes, while the lower percentage of error in the second case tends to 
support the view that the yellow color is dominant. ‘The method of analysis con- 
sists of the treatment in the first instance of the group of gravid adults displaying 
the color assumed to be recessive, and of an entirely independent study of the 
DD-+DR class, to see how closely the observed facts correspond to deduction. 
Obviously, the chief difficulty in procedure is to determine how much adjustment 
is made necessary on account of the small average number of young in the brood- 
chamber. 
PaPEIHA VALLEY. 
It is here that the bicolored shells are found; they are classified as red because 
of the presence of that color, even if it does not cover the entire shell. However, 
a source of error in the assignment of embryonic shells to their correct class arises 
from the difficulty of detecting the bicolored pattern in the very young individuals; 
this error would tend greatly to increase the yellow class of offspring at the expense 
of the other. Here the numerical relations of the two color-classes are reversed in 
the adult populations, as compared with the Oopu colony, the yellow adults form- 
ing 63.39 per cent and the red adults only 36.6 per cent. The yellow parents with 
young, counted once, are 47 out of 75, or 62.66 per cent; the similar red parents are 
28 in number, or 37.3 per cent. Their contents are as follows: 
(1) Red adults: red young, 13; red and yellow young, 7; yellow young, 8=28 
(2) Yellow adults: red young, 3; red and yellow young, 3; yellow young, 41=47 
Assuming that the red color is dominant, we begin with the contrasted indi- 
viduals that would be RR; in 63 per cent of these the mate would be a similar RR 
snail, or 29.6 cases to be taken as 30. The difference between their theoretical 
