Tea vers. — Distribution of Paryphanta in N.Z. 227 



is well known that slight differences in latitude often deter- 

 mine the range of many species, and therefore the compara- 

 tively restricted range of the different shells before you need 

 cause no surprise, more especially when we compare it with 

 the peculiarities in this respect which are found to exist in 

 other oceanic islands. The Sandwich Islands afford a notable 

 example of such peculiarity. They have yielded between 

 three and four hundred species of land-shells, all or nearly all 

 of which are said to be endemic ; and the average range of 

 any species (according to the observations of the Eev. Mr. 

 Gulick, the chief authority on this subject) is five or six 

 square miles at the outside, whilst some are restricted to but 

 one or two square miles, and only very few have the range of 

 a whole island. It is even said that some valleys, and often 

 each side of the same valley, possess then- own peculiar species. 



The case of Madeira is a somewhat singular one. Wallace 

 tells us that about fifty-two species of land-shells have been 

 found in Madeira and forty-two in the small adjacent island 

 of Porto Santo, but that only twelve are common to both 

 islands, though all, or almost all, are distinct from their 

 nearest allies in Europe and North Africa. 



Now, all this is very singular; and yet so great has been 

 the stimulus given to inquiry by the writings of Darwin that 

 we are gradually becoming acquainted, through the observa- 

 tions of a host of naturalists in all parts of the globe, with 

 means of dispersal of this class of animals which must have 

 acted for all time, and may fairly account for its present con- 

 dition of distribution. Darwin himself made many experi- 

 ments on the power of land-shells to resist sea-water, and 

 these were sufficient to show that it was quite possible for 

 them to be carried in driftwood for many hundred miles 

 across the sea, and this, according to Wallace, coupled with 

 their power of living for long periods without food, is, as I 

 believe, probably one of the most effectual modes of their dis- 

 persal. As an instance of such means I may quote the 

 following passage from Mr. Hickson's " Naturalist in North 

 Celebes." Speaking of the fact that many of the squirrels, 

 rats, and bats of the Philippine Islands and of Celebes are 

 identical, or very similar, and that this is not to be wondered 

 at, for that they could easily be drifted from the one island to 

 the other on drifting timber, he says that " the opportunities 

 afforded to arboreal animals to emigrate from one island to 

 another are not so infrequent as might be supposed. During 

 the heavy rains of 1882 the Wanada Eiver brought down vast 

 numbers of forest-trees, and many of these must have drifted 

 to sea with a considerable crew of squirrels, mice, caterpillars, 

 and other animals." And he mentions the remarkable fact 

 that after the eruption of Krakatoa, in 1883, a female green 



