ZOOLOGA OF FERNANDO NORONHA. 
475 
Planorbis, and an Ostracod, the latter also occurring in all the 
streams of any size. The remaining streams and puddles pro- 
duced dragouflies, a species of Gam-mams, and a few algee. One 
may compare this state of things with the freshwater fauna and 
flora of the other Atlantic islands. The absence of freshwater 
fish and amphibians is common to most small islands. 
Just as with plants, a considerable number of animals have been 
introduced by man into the islands intentionally and by accident : 
such, for instance, as the Gecko ( Hemidactylus mabouia), the 
American Cockroach ( Blatta americana ), and its curious parasite 
Evania, a spider, centipede, scorpion, rats and mice, and Sitoplidus 
oryzce. These, though usually plentiful on the main island around 
the houses, are markedly absent from the smaller islets. 
There are also many visitors which have arrived here by the aid 
of their wings, probably assisted by a suitable wind. They 
include a number of the peculiar terrestrial fauna, the land- 
birds and the insects. On looking over the lists of species 
taken here, we may note that the smaller birds are endemic, and 
a large proportion of the smaller insects. The small butterfly 
and almost all the moths are known from the mainland of South 
America, and the dragonflies are also widely distributed forms. 
All the winged fauna have a South-American facies, whether they 
are endemic or of wider distribution. 
There are other creatures unprovided with means of traversing 
the ocean and not introduced by man. They include the 
Amphisbcena, Skink, the freshwater and terrestrial Mollusca, 
and perhaps some of the feebler-winged and apterous insects, 
the endemic ostracod, Ac. 
The Planorbis, Gammarus, and Ostracod, all supposed to be 
endemic species, may possibly have been brought over on the 
feet of Wading birds, which migrate here. 
The presence of some others is more difficult to account for. 
The Mollusca are almost all peculiar, and the two that are not 
so are West-Indian. The Amphisbama and Skink are endemic, 
and allied not to Brazilian but to West-Indian forms. . 
It is commonly said that reptiles and terrestrial mollusks find 
their way across the ocean by secreting themselves, or their eggs, 
on floating trees, which are drifted to islands ; and though for 
several reasons this does not seem a satisfactory explanation of 
their distribution, yet the appearance of these animals here 
suggests this as the means by which they may have arrived. As 
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