74. VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
Among the 534 recorded individuals, 136 were barren; the embryonic contents 
of the other varied as follows: 
NG Gera anlywoumes 2 2 3 4 8 © FY B OD 
No. of adults: Bi fi GO 73 Gh 37 22 © BB f 
It seems that a given adult breeds intermittently and produces a series of off- 
spring after a period of reproductive rest. When the brood-chamber contains only 
three or four individuals, either they range from newly formed eggs to very young 
snails, or they stand at the older end of the series and are ready or nearly ready to 
be born. In the former case a resumption of breeding activity is indicated, while 
in the latter the parent is about to close a period of reproductive effort. 
Much variation in colonies also appears. In some cases, such as Moaroa, only 
50 per cent of the adults were gravid. Of 23 adults taken in Teohu, 20 bore young 
and eggs. Vaihiria and Vairaharaha are scarcely separated at their lower ends and 
are therefore so close that environmental conditions are practically the same; yet 
their gravid adults are 83.9 per cent and 91.3 per cent, thus differing markedly in 
their productivity at one and the same season. Again, Maara is next to Vaihiria 
on the east; all 3 of the adults taken were bearing, but there were only 3 off- 
spring in all—an average of 1. Treating the returns of this case as we did those 
for hyalina, it is found that for every 100 adult snails 74 are bearing the reproductive 
burden for the time and they produce 271 young; therefore 171 of this generation 
probably die before reaching reproductive maturity themselves, and hence elimina- 
tion would seem to be slightly more severe than in the case of hyalina. 
THE EVOLUTIONARY SIGNIFICANCE OF THE VARIATION AND DISTRIBUTION OF 
PARTULA CLARA. 
SUMMARY AND DISCUSSION. 
It now remains to bring together the important points of the foregoing detailed 
descriptions and to state clearly the general results of an evolutionary significance. 
The situation in this case is obviously very different in many respects from that 
of hyalina; it will become evident that the differences in question materially favor 
the establishment of definite conclusions regarding the history of clara and that 
such conclusions support and amplify the interpretation of evolution in the genus 
Partula, based upon the first case. The facts indicate that clara is a species which 
had been greatly reduced in numbers, but which subsequently recovered its vigor 
and increased in numbers, migrating into wide areas formerly unpeopled by it and 
differentiating often by mutation into numerous subordinate types in the course 
of its recent dispersal. 
I. Partula clara, which exists only in Tahiti, was formerly a rare species, while 
now it 1s relatively abundant in certain localities. In Garrett’s monograph (1884) 
he says that clara is “a rare species, found on foliage in the upper portions of the 
valleys in the southwest part of Tahiti.” In 1879, in a letter to Hartmann (ref. in 
