ON GENERATION. 209 



old nests, which, as useful for firing, are all made objects of 

 traffic by the proprietor ; the sum he mentioned to me exceeds 

 credibility. There was this particular feature which, as it refers 

 to our subject, I shall mention, and also as it bears me out in my 

 report of the multitudes of sea-fowl : the whole island appears 

 of a brilliant white colour to those who approach it, all the 

 cliffs look as if they consisted of the whitest chalk ; the true 

 colour of the rock, however, is dusky and black. It is a friable 

 white crust that is spread over all, which gives the island its 

 whiteness and splendour, a crust, having the same consistency, 

 colour, and nature as an egg-shell, which plasters everything 

 with a hard, though friable and testaceous kind of covering. 

 The lower part of the rock, laved by the ebbing and flowing 

 tide, preserves its native colour, and clearly shows that the 

 whiteness of the superior parts is due to the liquid excrements 

 of the birds, which are voided along with the alvine faces ; 

 which liquid excrements, white, hard, and brittle like the shell 

 of the egg, cover the rock, and, under the influence of the cold 

 of the air, incrust it. Now this is precisely the way in which 

 Aristotle and Pliny will have it that the shell of the egg is 

 formed. None of the birds are permanent occupants of the 

 island, but visitors for purposes of procreation only, staying 

 there for a few weeks, in lodgings, as it were, and until their 

 young ones can take wing along with them. The white crust 

 is so hard and solid, and adheres so intimately to the rock, that 

 it might readily be mistaken for the natural soil of the place. 



The liquid, white, and shining excrement is conveyed from 

 the kidneys of birds by the ureters, into the common receptacle 

 or cloaca; where it covers over the alvine faeces, and with 

 them is discharged. It constitutes, in fact, the thicker por- 

 tion of the urine of these creatures, and corresponds with that 

 which, in our urine, we call the hypostase or sediment. We 

 have already said something above on this topic, and have 

 entered into it still more fully elsewhere. We always find an 

 abundance of this white excrement in mews ; where hawks be- 

 smear walls beside their perches, they cover them with a kind 

 of gypseous crust, or make them look as if they were painted 

 with white lead. 



In the cloaca of a dead ostrich I found as much of this gyp- 

 seous cement as would have filled the hand. And in like 



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