132 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
specimens of the several years came from one habitable area. In 1906, however, 
owing to the severe cyclonic disturbance of February, the interior was very difficult 
of access on account of the fallen trees and tangled vegetation. Only the extreme 
outer fringe of the inhabited area was reached, which circumstance accounts in 
part for the small numbers obtained in the first year. As in Garrett’s time, amabilis 
is by no means abundant in this valley, a second reason for the paucity of material. 
The shells fall into the same color groups that were established in the case of the 
Fautaua colony, in each of the two modes of coil (plate 25, figs. 44 to65). Virtually 
all of the combinations of characters specified by P. 0. otaheitana are repeated in 
amabilis of Hamuta, although even a cursory examination shows that the general 
dimensions are different in degree, while furthermore the proportionate numbers 
assignable to the various subdivisions by no means agree with those in the Fautaua 
table. 
CoMPARISON OF SINISTRAL AND DEXxTRAL GROUPS. 
Following the order of treatment in the case of P. otahettana otaheitana, we may 
consider first the proportionate numbers of the direct and reversed snails (table 65). 
The 1906 series shows an astonishing preponderance of sinistral individuals, while 
the series of the other two years agree more closely with one another and with the 
figures for 1899, as given by Mayer. ‘The adolescent snails in my collections out- 
number the adults for 1906; when the two groups are combined the percentage of 
reversed individuals rises to the high figure of 74 per cent. 
TaBie 65.—Partula otaheitana amabilis, Hamuta Valley. Numerical relations of form-classes. 
Adults. Adolescents. Adults and EID EY OUIC 
adolescents. young. 
Series. SSS 
No. |Per cent.| No. |Per cent.| No. |Per cent.| No. |Per cent. 
190 9Nsinistralaaneeereeee 20 68.9 4 57.1 24 66.6 42 87.5 
dextraleeee reece 9 31.0 3 42.8 12 33.3 6 12S 
LOO /-sinistralemererieee 240 61.4 72 62.0 312 61.5 167 SU otf 
dextralher eee 151 38.6 44 37.9 195 38.4 112 42.2 
1906, sinistral........... 39 88.6 62 68.1 101 74.8 7 100 
dextralepeerreniere 15 11.3 29 31.8 34 25a 0 0 
1909-1906, sinistral...... 299 63.0 138 64.5 437 63.5 216 64.6 
dextralaerer ieelido: 36.9 76 35.5 251 36.4 118 35.3 
1899 [Mayer], sinistral...] ... 69 a Sides Ae aoe oe 73 
dextralieras| marae 31 AS Meee Sake eas Re 27 
Why the embryonic young of 1906 and 1909 should show so great an excess of 
sinistral individuals is difficult to conjecture. Such a result might be due to a 
higher rate of multiplication on the part of this type, and apparently some support 
for that interpretation is afforded by the figures for fecundity (table 66), which give 
in all cases an average above that for the dextral adults when the two form-classes are 
compared year by year. Yet when the average number of young for the entire 
series of a given year is taken into account, together with the percentage of gravid 
individuals in the whole series, it appears that the sinistral snails breed over a 
