zooLoar op fernando noronha. 475 



Planorhis, aud an Ostracod, the latter also occurring in all the 

 streams of any size. The remaining streams and puddles pro- 

 duced dragonflies, a species of Gammarus, and a few algse. One 

 may compare this state of things with the freshwater fauna and 

 flora of the other Atlantic islands. The absence of freshwater 

 fish aud 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), aud its curious parasite 

 Evania, a spider, centijiede, scorpion, rats and mice, and Sitoplidus 

 oryzcB. Tliese, though usually plentiful on the maiu 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 wiugs, 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 

 Amj}hishcBna, Skink, the freshwater and terrestrial Mollusca, 

 and perhaps some of the feebler-winged and apterous insects, 

 the endemic ostracod, &c. 



The Planorhis, Ganimarus, and Ostracod, all supposed to be 

 endemic species, may possibly have been brought over on the 

 feet of Wading birds, w hich migrate here. 



The presence of some others is more diflicult to account for. 

 The Mollusca are almost all peculiar, and the two that are not 

 so are West-Indian. The Amphislxena 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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