13S 1 he Irish Natutalist, April, 



Britain to Japan, we see an island dominion in some respects 

 remarkably like our own, in others strikingly different, but 

 which for my present purpose yields a resemblance, in the 

 fact that the number of land mammals found in Japan is 

 almost exactly the same as the number found in the British 

 Islands. So, if our seas proved a barrier to a general rush 

 from Siberia westward, it may be asked, did Japan's sea prove 

 a barrier to a similar rush, at an earlier period, from Europe 

 eastward ? At any rate, both groups of islands, at opposite 

 ends of a great continental area, agree in the common poverty 

 of their faunas compared with the faunas of the neighbouring 

 shores. 



To go through all the island faunas of the world would be a 

 large survey; but I would remind you what great stress 

 Darwin laid — as. also his great co-thinker Alfred Russel 

 Wallace — on the absence from what he called oceanic islands 

 of terrestrial mammals and batrachians, while birds andwinged 

 insects and bats, and some other creatures rather harder to 

 account for, such as lizards and terrestrial mollusca, were 

 frequently found to occur. As these islands were supposed by 

 Darwin never to have been connected with any continental 

 land, the point of interest with him was to find out how they 

 came to possess any fauna at all, and particularly how such 

 creatures as lizards and laud-snails, belonging to many dif- 

 ferent species, had reached and colonised islands far out in 

 the ocean that bad never, since they arose from its waters, 

 been connected with any continental shore. In his chapter 

 on that subject in the " Origin of Species " Darwin builds a 

 most fascinating argument, and suggests many agencies which, 

 he thinks, might, from time to time, help a little in the suc- 

 cessful dispersal of lizards and snails across large expanses of 

 sea. But I think the criticisms advanced by Dr. Scharff and 

 by other recent writers against what is called the " flotsam 

 and jetsam" theory are very destructive of its force. "Occasional 

 means of transport' may — indeed they must — sometimes be 

 successful ; but it seems to be almost certain that something 

 else is needed to account for the practically universal presence 

 of laud mollusca on oceanic islands, and the very general dis- 

 persion of small reptiles in similar spots. Modern thought 

 seems, therefore, to tend towards the view that there are no 



