NATURAL HISTORY OF THE DIATOMACE^E. 459 



wise, the alimentary canals of sea urchins and sea cucumbers, as they 

 are commonly called, but whose correct and scientific, although, perhaps, 

 at first more incomprehensible names are echinoderms and holothurians, 

 as well as many fish and countless smaller creatures inhabiting the 

 waters, both fresh and salt, will be found to contain the skeletons of 

 diatoms which they take in directly as food, or indirectly when browsing 

 upon the algae and other examples of aquatic vegetation. So the exami- 

 nation of the half-digested food, from the stomachs of these creatures, 

 will often repay the trouble of preparing it for the microscope. And 

 here is an appropriate opportunity of saying something with regard to 

 that remarkable and important substance which goes by the name of 

 guano, and which has proved to be an almost inexhaustible storehouse 

 for beautiful forms of diatomacese. Very generally this substance is 

 supposed to be the excrements of birds, which has accumulated in large 

 quantities during the lapse of many years upon the rocky islands in the 

 Pacific ocean and elsewhere, in latitudes where little or no rain falls to 

 wash out the organic matter. This substance has been used by the 

 inhabitants of the coast of South America from time immemorial as a 

 manure ; and, since it was introduced into Europe by Humboldt, in 1804, 

 it has been largely exported to that country and this, to supply the 

 exhaustion of our fields by the continuous crops necessitated by our 

 always increasing population. 



Some years since, the attention of the writer of this sketch was called 

 to the subject of guano, when engaged as an analytical chemist in exam- 

 ining fertilizers of different kinds; and thereafter, when studying the 

 diatomaceae and the application of a knowledge of them to geology, he 

 pushed his investigations still further, and at last came to the conclusion 

 that the popular prevalent notion with regard to the origin of guano was 

 erroneous. His ideas on the subject he embodied in a communication 

 made to the Essex Institute of Salem, Mass., on the 4th of January, 

 1869, an abstract of which will be found in the Bulletin of the Associa- 

 tion, vol. I, p. ii. Subsequently, with the Hon. E. G. Squier and Dr. 

 A. Habel, who had visited the celebrated Chincha islands, and there 

 observed some facts which confirmed the present writer's notions with 

 regard to it, he again brought the subject prominently before the public 

 at a meeting of the New York Lyceum of Natural History, held May i, 



