110 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
ductive rate proved to be slightly higher than in the same species of Guam, as the 
average embryonic contents numbered 3.72 as compared with 2.96 for the southern 
island. We may note that the proportion of eggs to young snails is about 1.4 to 
1, while in the Guam series it was 1.6 to 1; if the figures are taken at their face value 
this means that in Saipan the species was slightly more advanced in its reproductive 
cycle. By way of amplification table 59 records the complete distribution of the 
embryonic contents, eggs and young, both in tabular form and in summary. 
TABLE 59.—Partula gibba, Saipan. Recorded adults and their embryonic contents. 











Number of young. 
0 1 2 3 4 5 
Number of eggs: 
Oi os kas otal hve cake «ote 388 73 32 1 er 
1 ioeclohetets «Ghee Sateents ite 90 191 186 21 z 1 
23 Be Te ee leet ae 95 266 ao fe 5 eens 
So wnt iereeiciecareaateieeas ect 41 168 258 70 6 ce 4,813 eggs. 
AUN. . Soctesaleue Remsen isnelack 19 68 103 37 1 Fact 
Dis aeua abshorats tetera a oibabeta coe 2 10 15 8 
Ge oie o'o. Pas aden re sie pions oe 1 3 
635 777 948 208 14 
PP OtAL co. oie San ste sueree oie lieatmusinre aoe a 2,585 records. 
3,368 young. 

Embryonic contents. 
Summary. 
Number of adults (=2,585)... 
More frequently than in Guam the order in which the embryonic contents lie 
in the brood-pouch is irregular, in the sense that less-developed or undeveloped 
items are nearer to the birth aperture than older ones. In all, 45 instances were dis- 
covered, as enumerated in table 60. Particular interest attaches to the two unmis- 
takable instances in the Chalankiya series where “egg-young”’ (indicated in the 
table as ey) were found beyond much older embryonic snails, because in these 
cases we have true “‘anachronisms” where a capsule containing a newly fertilized 
egg is actually pushed past one formed earlier; in by far the majority of instances 
the “‘egg”’ beyond a “young” snail is really a capsule devoid of an inclosed zygote 
or it contains a fertilized germ which has failed to develop. 
The data of heredity are lastly to be considered. Here as everywhere else in 
the Mariana species the embryonic snails are universally dextral like their parents. 
While it is not permissible to assert that sinistral offspring are never produced, 
the material in hand fails to disclose a single instance of a reversal in spirality. 
The qualities of color in gibba are not such as to provide ideal material for 
the determination of the hereditary relations between parents and offspring in 
such respects, but nevertheless there is positive proof that at least some of the 
color-classes interbreed. The embryonic shells appear in two phases which are 
quite clearly contrasted; they are either very light and almost colorless or they 
