3G6 MOLLUSKS OF THE GALAPAGOS — STEARNS. 



winter or rainy season oc(;urs of nnnsual anil extraordinary precipita- 

 tion when the swollen currents exhibit torrential energy.* 



Peru has numerous streams in common parlance of insignificant i)ro- 

 portions and of little value for other than irrigating purposes. These, 

 too, in seasons like the above, become imiK)rtant by reason of the 

 damage resulting from their catastrojjhic action. 



And still farther to the north, along the westerly slopes that drain 

 into the Pacitic, we may reasonably assume contributions aie nuide to 

 the general drift material that rivers ordinarily carry to the sea, and 

 which, being within the range and inlluence of the west Mexican cur- 

 rent, are likely ultinuitely, in part at least, to be borne seaward along 

 its westerly course. 



A single tree of large si/.e might carry with it not only nu)lluscan 

 ami insect forms mature, living, or in the e<*g, of several species, but 

 also living individuals of many vertebrate forms that found refuge or 

 safety nj)on it, sominvhere along it,s course from its native forest home 

 to the point where it found final lodgment, or was cast ashore; thus 

 if the environmental conditions were at all favorable, would be i)lanted 

 the foundation of a colony whi<'h would extend its territory so far and 

 in such directions as were most congenial. The area of surface above the 

 water furnislied by the main trunk of such a tree, and the drift consisting 

 of various material entangled in and among its branches, would be amply 

 suflicieiit in the nuitters of s[)aceand security, for the transportation of 

 nmny animal forms; of these such as possessed sufficient vitality to suc- 

 cessfully meet the contingencies of the voyage in the way of hunger, 

 thirst, et(!., would become the progenital stock in new regions more or 

 less distant from their original haunts, where, under the steady but mod- 

 erate pressure of new environmental conditiims, in the cimrse of gciu'ra- 

 tions a new fades would be gradually brought about, dtn'cloped in or 

 given to the more plastic, and we should have what are called new 

 species. 



GENERATIVE (lAPAOITY ANT) VITALITY OF LAND SNAILS, ETC. 



The prolific generative capacity of the land snails and their extreme 

 tenacity of life are to be considered in connection with their geograi)h- 

 ical distribution and establishment in new areas under the circum- 

 stances and conilitions described above, as well as in the matter of 

 ])robable aerial distribution, which last has never received sufficient 

 consideration as i)laying an impoitant part, or any ])art whatever, as 

 an agency in dispersing or distributing animal life or extending s]»e- 

 citic areas or creating new ones remote from those ])reviously existing. 



"The number of eggs produced varies in the genera and species," 

 says liinncy, '• in the sajne projjortion as the dangers to which they 



* It 'vas the occurrence of such a wintor as tins that, dostroyod the botanical gar- 

 den t)f my friond the lato Thomas Bridf^es, wluiso I'jstablishmtut was wilhui JGood 

 Eaufio of cue of these C'hileaju strcajuis. 



