30 The Philippine Journal of Science 1917 
facts the American origin of all the Cocoineae can no longer be 
considered as absolutely proved. 
THE ASSOCIATION OF BIRGUS LATRO WITH THE COCONUT PALM 
Birgus latro, the huge robber crab which is widely dissem- 
inated throughout Asiatic archipelagoes and Polynesia, is found 
also in the Palmyra Islands, and from Mr. Rock’s account it 
abounds in that group along with other crustaceans. I have 
already made use of the association of Birgus with the coconut 
palm,‘ as an argument against the suggested American origin of 
Cocos nucifera; for it seems to me to be inadmissible that Birgus 
could have been specifically evolved independently of the coconut. 
Without coconuts it would have nothing to live upon; whereas, 
if this association did not exist, the peculiar and special forma- 
tion of this crab’s prehensile organs—thanks to which it is able 
to grasp and break open the coconuts, which are its only means 
of subsistence, to say nothing of its climbing the trees which bear 
them—would surely not have come into existence. In any case, 
it seems to me that this association can hardly have originated 
in those eastern valleys of Peru wherein Cook insists that Cocos 
_ nucifera had its origin. It is also a noteworthy fact that Birgus 
is found in association with the coconut palm even in places far 
distant from each other and to which this palm might be held 
to have spread in a natural way, such as the Keeling Islands in 
the Indian Ocean and the Palmyra group in the Pacific. 
I do not know if Birgus has been found in the Cocos Islands, 
in the Pacific, where however I should not be surprised if it 
existed ; because, although the adult Birgus is a creature adapted 
to a terrestrial life, in the larval, or “zoaea,” state it has a 
pelagic existence and, therefore, can be carried enormous dis- 
tances. Nevertheless, Birgus seems to be absolutely unknown 
on the American shores of the Pacific. This gives me the oppor- 
tunity to suggest the hypothesis that the long-enduring biological 
connection between Birgus and the coconut palm, which in the’ 
course of time has had the power of modifying certain organs 
in Birgus, likewise, has had the same influence in causing the 
coconut palm to assume some peculiar features. I allude to the 
extraordinary thickening of the pericarp, which from a teleo- 
logical point of view has been attributed either to the advan- 
tage it gives to the fruit when floating, by which its dispersal is 
favored, or to the importance of deadening the shock when it 
falls from the tree. This secund opinion is also shared by 
* Ann. Bot. Gard. Buitenz. Suppl. 3 (1910) 804, 
