DIATOMS IN THE OCEAN. 99 



which have been very recently published by Dr Wallich. 

 He has ascertained that they exist in a free, swimming 

 condition, in various regions of the ocean, and at various 

 depths from the surface downward ; that their multitude 

 is incalculable ; and that they afford sustenance to im- 

 mense numbers of molluscous and crustaceous animals, 

 which in their turn constitute the food of the most sioan- 

 tic creatures of the deep. Dr Joseph D. Hooker had no- 

 ticed the vast profusion of Diatomacece in the Antarctic 

 Sea ; and he was struck by the conspicuous appearance 

 presented by their masses imbedded in the substance of 

 the ice, or washed up on its surface by the action of the 

 billows. 



Dr Wallich found the surface of the Bay of Bengal and 

 the Indian Ocean to be crowded with masses of minute 

 life, forming yellow streaks, flakes, and tufts, intermixed 

 with glistening points, which, when examined, proved to 

 be recognisable forms of the organisms in question. The 

 mighty scale on which the Diatomacece really exist, did 

 not become manifest, however, until he reached the At- 

 lantic, between the Cape and St Helena.* 



" It was here that, for many degrees, and in bright, 

 breezy weather, the ship passed through vast layers of 

 sea-water so thronged with the bodies of a species of 

 Salpa {S. mucronata) as to present the consistence of a 

 jelly. What their vertical limits were, it was impossible 

 to discover, owing to the speed at which the ship was 



* See Annals Nat. Hist, for Janvxiry 18G0; and Quarterly Journ. Mia'. 

 Set. for January 1860. 



