50 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
young at any one time. The average number of young and eggs is 3.75 for each 
bearing adult and 2.44 for each individual of the entire adult population of nearly 400. 
The same table shows that there is no well-defined season for breeding in the 
case of this species, for the data of 1906 are substantially the same as those relating 
to 1907, 1908, and 1909, although collections were made during the last of the wet 
season in the first-mentioned year, and during the alternating period of less rainfall 
during the last-named. From the facts relating to P. otaheitana, presented in a 
subsequent section, it is certain that in that form there is greater reproductive 
activity at the advent of the wet season. Apparently hyalina does not agree with 
otaheitana and other species in this respect. 
The data may be rearranged so as to bring out any differences in fecundity 
that may exist in colonies of diverse regions (table 15). The figures show that 
the rate of multiplication is not the same in the several major divisions of Tahiti, 
nor is it uniform in any series of contiguous valleys lying in one ecological section, 
as a more detailed comparison shows. In brief, the reproductive phenomena under 
consideration vary like numerical abundance and structural characters, without ref- 
erence to any external circumstances that can be discerned. Within the limitation 
of its specific characters, each colony constitutes an independent type. 
Tas_eE 15.—Partula hyalina. Tahiti. Statistics of fecundity. 
ANNUAL OBSERVATIONS. 
| | 
Year of | No. of | No. of No. of | Per cent No. of | Average | Average 
b: ti tati record ravid ravid YOUns for for 
observation. stations. cords. | gravid. | gravid. | 7 4 Sebel aemntil all. 
L9OOG He Seis | 16 143 88 61.5 330 3.75 2.30 
OY (RetsopnGonoc 31 202 137 67.8 519 3.78 2.56 
19083 eee eye dercte | 6 24 14 58.3 60 4.28 250) 
IOS os oaxorod so | 11 28 19 67.8 60 $3115) 2.14 
All years....... 64 397 258 64.9 969 309) 2.44 
REGIONAL CLASSIFICATION. 
Quadrant: 
INCE Soc0000 21 202 129 63.8 464 3.59 2.29 
Wiestsacrersieis 7 47 26 BS583 72 2.76 1.53 
Southeeeeeee 17 46 27 58.6 107 3.96 DROZ, 
aster enierk 8 44 32 72.7 136 4.25 3.54 
Malarapurewrere 11 58 44 75.8 190 4.31 3.27 
Whole island... . 64 397 258 64.9 969 3.75 2.44 
FECUNDITY AND ELIMINATION. 
A question of much biological interest is concerned with the possibility of a 
relation between the high average fecundity of hyalina and the process of elimina- 
tion by which the numbers of new-born young become reduced. We may justly 
assume that the species under consideration has attained a condition of approximate 
equilibrium as regards its numerical abundance, so far as this depends upon the 
incident action of external agencies. We may also regard the collections as repre- 
sentative of the whole island-population of hyalina. These collections comprise 
