PARTULA OTAHEITANA. 173 
By assumption, the 74 gravid yellow adults are RR in composition, while the 
121 red adults are DD+DR in a proportion as yet undiscovered. 
The yellow parents with young will have mated with DD, DR, and RR adults 
according to the chance possibilities, and in the case of the RRXRR mating the 
number can be ascertained; it is 36 per cent of all cases, which follows from the 
fundamental data given in table 114. Specifically, the number is 36 per cent of 74, 
or 26.64, taken as 27. These would bear yellow young only (RR XRR=RR-+RR). 
Empirically, however, we find 39 gravid adults of this class; the excess of 39 over the 
theoretical number of 27, or 12, comprises these RR adults which have mated with 
DR and not RR, but their young are too few to represent both kinds of expected 
offspring, as they would according to theory (RR&XDR=DR-+RR); such adults, 
if mated with DD, would have borne red young only, and no yellow young. Hence 
we must correct (2) by transferring to the middle class the 12 RRXDR, with the 
following result: 
(3) Yellow adults: red young only, 19; both kinds, 28; yellow young only, 27=74 
But we found that certain adults, bearing yellow young only, amounting to 12 
out of 39, really belonged to the middle class; undoubtedly some of the yellow adults 
bearing red young only would produce yellow offspring as well, if the embryonic 
contents were more ample. Such individuals are RR in composition by assump- 
tion, and their mates would have been DR; they, too, should be placed in the 
middle class. The only basis for estimating their numbers is the fractions trans- 
ferred from the third to the middle class, or %. Effecting the transfer of the 6 
individuals thus indicated, (3) becomes: 
(4) Yellow adults: red young only, 13; red and yellow young, 34; yellow young only, 27=74 
The numbers in these three classes stand for the matings of RR parents with DD, 
DR, and RR snails, respectively, and hence the relative numbers of DD and DR 
snails in the class of 121 red parents are discovered and defined. 
The second part of the present Mendelian analysis consists of a study of the 
red class of parents classified as in (1), to see how closely their empirical numbers 
correspond to expectation when the proportions are actually what the treatment of 
the yellow snails has disclosed, namely, 13:34:27 respectively. As we are now pro- 
ceeding on the assumption that the yellow color is the recessive member of the pair, 
the 121 red snails are DD and DR in genetic composition in the proportion of 
13:34, Or 33.47 and 87.52 individuals, taken as 33 DD and 88 DR. 
The 33 red snails of the DD group have had mates of unknown genetic composi- 
tion, but which would be DD, DR, and RR according to chance proportions. Still, 
the characters of the unknown mates are not important here, for in all cases the 
offspring would be red in color, for an RR combination among them would be 
impossible. Hence at least 33 of the red parents with red young only in (1) are 
accounted for. 
The 88 DR red parents would also have mated with DD, DR, and RR snails 
according to the chance possibilities derived from the analysis of the yellow class, 
as formulated in (4). The cross of DRX DD would occur in # of the 88 cases, or 
