12 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
it is not at all probable that the animals could remain alive during the time required 
for the slow journey of their rafts to another habitable area, under the influence 
of the winds and currents. 
It is in other ways that the inorganic factors here discussed affect the lives of 
the present research organisms, so far as they are involved in the whole combination 
of circumstances which collectively determine the amount of rainfall and degree of 
humidity. 
TEMPERATURE AND RAINFALL. 
By virtue of their situation within the tropics, the Mariana Islands are very 
warm and humid, and hence their forested areas are virtually ideal habitations for 
snails of the genus Partula. 
TABLE 2.—Statistics of temperature for 1902 at Agana, Guam (after Safford). 







ae a 
Month. 
M Absolute | Absolute Mean Absolute | Absolute Mean 
ean. ; aa Mean. 2 a F 
maximum. | minimum. |daily range. maximum. | minimum. |daily range. 
Janearys.. thik ise es Sem 79 86 70 8 26.1 30.0 oH ID | 4.4 
Februlary2etc.cde 6.2. sere 80 50 71 8 26.7 30.0 2127 4.4 
Marchi. «Senne tines tte 80 87 72 10 26.7 30.6 1 Ee | 5.6 
Apiit yor ccak ees oteets 81 87 73 8 212 30.6 22.8 4.4 
Mawyi. ici nyeackeicititon tenes 82 88 72 9 21-8 Slee | 2752 5.0 
JUNE. 2 apices creteipaly 82 90 73 10 27.8 32.2 22.8 5.6 
July ieee eee 81 90 75 9 Dine 32.2 23.9 5.0 
ANGUS ic. avcs cay eee 81 88 74 9 Zee ee | 2305 5.0 
September icivvyt «soe 42h 80 87 73 11 26.7 30.6 j9 | 6.1 
OCHIDER oan kee eens 80 88 70 10 26.7 Ka Wee | 2 5 6 
Novemberzs.. hes te ces 79 85 69 11 26.1 29.4 20.6 6.1 
December, ceatints seh 78 85 66 9 25.6 29.4 18.9 5.0 
Annual maximum....... 82 90 ea 17 27.8 S2a2 Sec, 9.4 
Annual minimum....... 78 es 66 3 25.6 5 FE 18.9 17 
Mearite be. con aaa 80 87 72 9 26.7 30.6 fy Se? 520 






Not only is the climate warm, but it is remarkably equable as well, for the 
limits of diurnal and annual variation are unusually narrow. The exact figures for 
the capital of Agafia during the illustrative year of 1902 are given in table 2, which 
presents the substance in modified form of the temperature table in Safford’s 
volume; the organization of the records, as stated by Safford, was the work of 
Cleveland Abbe, Jr. The figures show a high general temperature with a gradual 
increase from January to June, and a subsequent regular decrease to December. 
The general monthly mean, the absolute maxima, and the absolute minima are 
entirely consistent indications of a long, slow, and low thermal pulse throughout the 
year. The difference between the absolute extremes for the year is astonishingly 
small, amounting as it does to only 8.4° C. 
It is to be kept in mind that the foregoing data were acquired at the single 
station at Agafia in Guam, and that the actual records taken in other parts of the 
island would assuredly differ in absolute figures. Clearly the forested areas are 
cooler than the capital town, whose roads and avenues bear little vegetation, if any, 
while furthermore it rests under the lee of hills which cut off the breezes from many 
quarters. Then, too, the influence of altitude in the higher areas is positive, 
