PARTULA OTAHEITANA. 299 
of occurrence. The newer type, when such has arisen, may increase in numbers 
so as to overwhelm the original kind, as in the case of crassa occidentalis, or the 
mutations may be only abortive steps toward the production of a new complex of 
qualities. 
V. From the present study, the congenital factors of variation seem to be 
paramount in comparison with the “environmental” influences affecting the snails. 
Doubtless there are few who would hold external circumstances accountable for the 
existence of different combinations of species in different localities, such as hyalina 
and otaheitana in Fautaua Valley, and hyalina, clara, nodosa, and otaheitana in 
Punaruu Valley. It is equally difficult to discern reasons for regarding diverse 
combinations of varieties as the products of one and the same environment, such as 
rubescens and affinis in Papenoo, rubescens, affinis, and sinistrorsa in Apirimaue, or 
simistrorsa and affinis in Vavil, when a few miles away in Aiurua the associates are 
rubescens and affinis. 
As to subvarieties, the sporadic occurrence of reversed or peculiarly banded 
affinis in widely separated localities could scarcely signify the operation of identical 
external factors in such places and not in the intervening territory; dextral sports 
produced in greater or less abundance in certain colonies of sinzstrorsa and sinistralis 
surely can not arise except through the operation of congenital factors that are 
independent of the environment. 
But it is not necessary to review the whole case at length, for in many of the 
foregoing pages the significance of the facts as observed has been pointed out. 
Brought down to their most succinct expression, the general conclusions are: 
(1) The negative statement that no differences in the environmental factors 
affecting the Partule can be discovered which would account for the production of 
diverse but intimately related forms in two contiguous valleys, such as typical 
crassa and crassa occidentalis in Orofere and Aoua Valleys, respectively. 
(2) The argument from the positive observations that in species X the colonies 
of two valleys are alike, while in the associated species Y the snails of the same areas 
are unlike. It is merely an appeal to ignorance to contend that, because two dis- 
tinguishable types occur in neighboring localities, there must be environmental 
factors for the observed differences; but even this contention breaks down when 
individuals of a mutant group, like dextral simistrorsa, appear in a valley along with 
their unchanged relatives. Ina word, the role of the environment is to set the limits 
to the habitable areas or to bring about the elimination of individuals whose qualities 
are otherwise determined, that is, by congenital factors. 
VI. It remains only to bring together general statistical summaries relating to 
the standard characters of the otaheitana shells. The figures for the several varieties 
are given in table 251, while table 252 shows the ranges and the means of the char- 
acters in both the sinistral and dextral divisions of each variety. Too much sig- 
nificance must not be attached to the data in certain cases, such as that of sinistral 
affinis, for the constituents are few and are widely scattered; similarly, the dextral 
groups of both sznistrorsa and sinistralis are locally represented, and are to be 
