30 



proportion of the crystalline to the earthy portions ; and the peculiar 

 nodulated character the latter exhibit could not be imitated by sand 

 or such-like impurities. 



Finding the examination of guano as an opaque object, with 

 low powers, not altogether satisfactory, I had recourse to higher ones, 

 and viewed it as a transparent object, moistened with water. This 

 view quite unravelled the nature of many of the bodies, which, with 

 a lower power it was quite impossible to understand. 



In this state we can readily see that guano is composed of organized, 

 crystalline and mineral matters. 



The organized appear to be fragments of dried flesh, apparently 

 that of birds or fish, as the characters of the muscular fibre justify 

 the supposition. 



Very minute fragments of shells, and abundance of spicules of 



' sponge, of two or three kinds ; and perhaps, what is most singular, 



very many specimens of animalcules belonging to the genera Actino- 



cyclus, Gallionella and Coscinodiscus, especially in that from Ichaboe, 



though I have not yet detected many in the Peruvian. 



When guano is digested in concentrated nitric acid, violent effer- 

 vescence takes place, and most of its constituents are dissolved, and 

 there only remain the siliceous, which exhibit clearly the animalcules 

 and sponge-spicules. 



Seeing guano composed of such various elements, it becomes a 

 matter of speculation from whence several of them are derived, and 

 in the first place the particles of muscular fibre, which appear to be 

 those of birds and fishes. It is easily to be imagined, as the latter 

 are so frequently devoured by the birds that inhabit these guano- 

 islands, that portions of the flesh were passed through the digestive 

 organs imperfectly digested, and were voided with the excrementitious 

 matters. If it be the muscular fibre of birds, it is possible that its 

 origin is from the death of the birds, whose flesh becomes after a 

 while intermingled with the guano, many specimens of birds being 

 dug up in a dried state, having suffered very little from decomposition. 



The siliceous animalcules and sponge-spicules, it would seem, be- 

 come present in the guano, from, firstly, being devoured by fishes, 

 whilst adhering to sea-weeds or mingled with the sand, and secondly, 

 the fishes being devoured by the birds, they are voided with the ex- 

 crementitious matters of the latter. As the guano localities are always 

 above the level of the sea, and the species of animalcules yet disco- 

 vered are all of the character that inhabit the bottom of the ocean, 

 the most probable reason for their occurrence is that above described. 



