PARTULA RADIOLATA. 57 
material was collected during the 2 months’ interval from June 28 to August 28. 
If production diminished or ceased during the months of lower temperature and 
lesser rainfall, to be resumed with the vernal intensification of these influences, 
then the number of eggs and young would sensibly increase with the passage of 
time thereafter. The period of field-work was divided into 8 time-classes of 7 days 
each, beginning with the arbitrary date of June 29. With the time-elements thus 
fixed, correlations were worked out between these elements and the numbers of 
gravid individuals in the several series, and also between the time-elements and the 
numbers of eggs and young in the parental brood-pouches. Twenty-one local 
series were sufficiently large to be used; the others were discarded because they 
were too scanty or, as in the case of the Tarague and Inarajan collections, because 
too long an interval elapsed between the actual collection of the animals and the 
time of their preservation, during which many of the advanced embryonic young 
escaped, thus invalidating the returns for the present purpose. 
Employing the standard methods for the determination of the coefficients of 
correlation, the results are as follows: 
Correlation between lapse of time and per cent gravid: + 0.1696 + 0.0 
Correlation between lapse of time and number of eggs: + 0.3976 + 0.1239 
Correlation between lapse of time and total embryonic contents: + 0.5279 + 0.1062 
The first coefficient shows that there is only a slight positive increase in the 
number of bearing adults, which means that reproductive activity had been gener- 
ally resumed somewhat earlier than the arbitrary date of June 29, when field-work 
was begun. The second figure proves that the production of eggs continues and 
increases slightly with the progress of the weeks. The third figure, taken in con- 
nection with the second, signifies that the young snails increased greatly in num- 
bers during the period of collection and observation more rapidly than the eggs. 
Therefore the onset of the fertile period must have been somewhat earlier than 
June 29, which is corroborative of the point established by the first correlation. 
Referring back to the discussion of the climatic factors (Chapter I), we are justified 
in stating that with the month of May the older animals of this species resume 
reproductive activity and the full-grown virgin individuals begin their fertile life, 
with general unanimity throughout the island; doubtless it is the increase of mois- 
ture especially that is the major factor of their reactions. 
The final subjects for which the embryonic materials are valuable are the 
phenomena of heredity and the question as to the genetic inter-relationships of the 
distinguishable color-classes. The embryonic snails are well advanced before their 
birth, and various characters of the shells are well expressed. On one point there 
is no uncertainty—the offspring are dextral without a single exception, like all of 
their parents and all of the adolescent individuals; there is no sporadic production 
of young with the opposite coil, as in P. nodosa and certain varieties of P. otaheitana 
of Tahiti. 
A large amount of material is available for the study of the heredity of the 
color characters, inasmuch as the colors of all of the young snails were noted when 
they were dissected out of their respective parents. It is well to state at the outset, 
