GENERAL FEATURES OF POLYNESIAN REALM IN RELATION TO DISTRIBUTION. 07/ 
Huahine in terms of Raiatea-Tahaa, and Tahiti in terms of Huahine, for coral- 
limestone is lacking on the borders of the strait between the two parts of Huahine 
as it is on the Isthmus of Taravao connecting lesser and greater Tahiti. But in 
any case, the complete biological survey of the group is rendered unusually interest- 
ing in view of the well-marked degrees of isolation and proximity displayed by the 
several land-masses, with which the degrees of resemblance or diversity manifested 
by the Partule may be correlated. 
As to the other islands of the group, little need be said, for they do not enter 
into the present investigation. Mehetia and Maupiti are small volcanic cones, 
with coral reefs. Most of the rest are coral atolls of circular or oval outline, while 
Makatea is an uplifted mass of coral limestone about 200 feet in height, exemplify- 
ing a kind of island that reaches its finest development in Vavau of the Tonga 
Group. Three contrasted geological types of islands, therefore, are represented in 
the Society Group; in the rest of Oceania the only additional type is the larger and 
older land-mass like that of Viti Levu of the Fiji Group. The islands that bear 
Partule are the larger ones of the “high” or volcanic type, separated by distances 
(table 3) that are to be taken into full account in discussing the biological relations 
of their species. 
TaBLeE 3.—A pproximate distances between islands of the Society Group, 1n geographical miles. 
Island. Moorea. | Huahine. | Raiatea. Tahaa. Borabora. 
shahitienernrnicte 10 90 112 120 136 
IMiooreanaeeein Sf 70 92 100 116 
Huahine....... oe bis 19 24 30 
Raiateasernnnne 28 3H ne BS) 20 
Ma haart crete “0 as oo oS 6 
The topographical features of Tahiti, representative of those displayed by 
practically all of the “high” islands inhabited by Partule, are to be dealt with 
in detail in Chapter II; hence only a few points need be noted here. The cen- 
tral area of the main division, Tahiti nui, is occupied by a broad crater valley 
(Papenoo), surrounded by high ridges, save where the basin is continued outwards 
to the coast. On the outer slopes of the great crater boundaries, streams have 
eroded other valleys of larger and smaller size, among which at least four grades 
will be distinguished beyond. These radiating valleys are arranged with almost 
mathematical regularity, both in Tahiti nui (plates 5a and 0b) and in Taiarapu 
(plate 6a), which repeats the general features of the greater element. Partule do not 
occur on the ridges, but are restricted almost entirely to these radiating valley areas 
by a complex of factors which are climatological in their real nature, but whose 
combined effects are such as to establish the stated distributional relation to topo- 
graphic features. 
WINDS, TIDES, CURRENTS. 
In discussing the factors that might exert an influence on the distribution of 
island organisms, the currents and winds must be recognized as possible agents of 
transportation and dispersal, even though, in the present case, their effects are 
negligible. 
