50 EAMBLES OF A NATURALIST. [Ch. HI. 



surface, were in a constant state of change, the colour com- 

 ing and going, from alternate contraction and expansion of 

 the pigment vesicles, without any direct • irritation. When 

 pale, the colour could be made to re-appear by drawing the 

 finger along the skin, but the power of contraction appeared 

 to be lost when the vesicles had been cut through. As it 

 lay on the table during the night, I cast my eye upon it, 

 and observed that it was luminous — a glow of whitish light 

 irregularly illuminating its whole surface. At this time it 

 was quite dry, and the luminous appearance was not altered 

 by passing my finger over it. 



On enquiring for shells, a good many were by degrees 

 brought to us, chiefly consisting of common cowries and 

 harps, and olives of several large and handsome varieties of 

 Oliva erythrostoma ; but nothing else could we obtain here, 

 though, if we had remained longer, it would perhaps have 

 been possible to have procured others. 



All these islands appear to be very destitute of trees ; and 

 standing on the high ground of Observation Island, on the 

 opposite side of the harbour, I looked in every direction 

 for a tree or bush, in vain. Although, however, the volcanic 

 structure of the island is not favourable to the growth of 

 wood, many very pretty flowers abound, the commonest of 

 which is a species of Cassia. Probably on account of 

 the deficiency of wood, very few birds were to be seen. A 

 few terns flew about the harbour, and some summer snipes 

 (Totanus) were seen occasionally. The commonest bird was 

 the tree-sparrow (Passer montanus), abundant everywhere 

 in the East, where it takes the place of the common sparrow 

 of Great Britain (P. domesticus) ; and besides these, I 

 observed, a small shrike, and a number of larks (Alauda 

 ccelivox) upon Observation Island, whose habit and character 



