210 ON GENERATION. 



manner the same substance abounds in tortoises and other 

 oviparous animals; discharged from the body it soon concretes 

 either into a friable crust, or into a powder which greatly re- 

 sembles pulverized egg-shells, in consequence of the evaporation 

 of its thinner part. 



Among the many different kinds of birds which seek the Bass 

 island for the sake of laying and incubating their eggs, and which 

 have such variety of nests, one bird was pointed out to me 

 which lays but one egg, and this it places upon the point of a 

 rock, with nothing like a nest or bed beneath it, yet so firmly 

 that the mother can go and return without injury to it ; but 

 if any one move it from its place, by no art can it be 

 fixed or balanced again ; left at liberty, it straightway rolls off 

 and falls into the sea. The place, as I have said, is crusted 

 over with a white cement, and the egg, when laid, is bedewed 

 with a thick and viscid moisture, which setting speedily, the 

 egg is soldered as it were, or agglutinated to the subjacent rock. 



An instance of like rapid concretion may be seen any day at 

 a statuary's, when he uses his cement of burnt alabaster or gyp- 

 sum tempered with water ; by means of which the likeness of 

 one dead, or the cast of anything else may be speedily taken, 

 and used as a mould. 



There is also in like manner a certain earthy or solid some- 

 thing in almost all liquids, as, for example, tartar in wine, mud 

 or sand in water, salt in lixivium, which, when the greater por- 

 tion of the water has been dissipated, concretes and subsides ; 

 and so do I conceive the white sediment of birds to descend 

 along with the urine from the kidneys into the cloaca, and 

 there to cover over and incrust the egg, much as the pavement 

 of a mews is plastered over by falcons, and every cliff of the 

 aforementioned island by the birds that frequent it; much also 

 as chamber utensils, and places where many persons make water, 

 become covered with a yellow incrustation ; that substance, in 

 fact, concreting externally, of which calculi in the kidneys, 

 bladder, and other parts are formed. I did formerly believe 

 then, as I have said, persuaded especially by the authority of 

 Aristotle and Pliny, that the shell of the hen's egg was formed 

 of this white sediment, which abounds in all the oviparous ani- 

 mals whose eggs are laid with a hard shell, the matter concreting 

 through contact with the air when the egg was laid. And so many 



