On Oceanic Infusoria, Liviny and Fossil. 159 



now known, whose forms are so minute that they ai'e individually in- 

 visible to the naked eye, and only appreciable when collected together in 

 masses, is very areat; and the cataloojue is daily enlaroino- as the waters 

 of the sea, and of lakes and ponds, are more carefully subjected to ex- 

 amination. What to the naked eye seems like a green or brownish 

 slimy scum, attached to the stalks of water-plants, or floating on the 

 surface of stagnant pools, displays to the microscope a series of ele- 

 gant and curious forms, endowed with a most perfect symmetry and 

 delicate structure of parts, each acting in the circle of its narrow 

 sphere as perfectly as the more bulky creations above it. The great 

 work of Ehrenberg has made the forms of many of those curious 

 creatures sufficiently known ; and a most elaborate monograph of a 

 portion of them,* recently published in this country, has added much 

 to the general history of the subject, while it affords to British stu- 

 dents exquisitely-accurate figures and careful descriptions of all the 

 British species of the group illustrated. The plants included in this 

 microscopic world are classed by botanists under two families, the 

 Desmidese, which exclusively inhabit fresh water, and the Diatomacese, 

 a great number of which are marine. The forms of these minute 

 organisms are strange ; they exhibit mathematical figures, circles, 

 triangles, and parallelograms, such as we find in no other plants, and 

 their surface is often most elaborately sculptured. Isthmia obliquata 

 is found in spring and early summer on the stems of many of the 

 filiform algae, where it forms little glittering tufts a line or two in 

 height. It has been brought from many distant parts of the world, 

 both of the Atlantic and the Pacific Oceans. Many other species 

 accompany it in our own and other seas. The Licmophora or Fan- 

 bearer is one of the most beautiful of our native kinds, and is very 

 common in April and May on the leaves of Zostera, as well as on 

 many of the smaller algse. It is very generally distributed round 

 the British Coasts, forming gelatinous masses of a clear brown co- 

 lour on the plants it frequents. Under the microscope, however, its 

 colours are much more gay, a yellow shade, variously banded and 

 marked with deeper-coloured spots, tinging the fan-like leaves, which 

 are borne on slender threads transparent as glass. The pieces or 

 joints of which these plants are composed are called frustules ; and 

 each frustule consists of a single cell, whose coat is composed of a 

 very delicate membrane made of organised silex. That these plants 

 have thus the power of withdrawing silex or flint earth in some 

 manner from the waters of the sea, and fixing it in their tissues is 

 certain, but the exact method in which this is effected has not been 

 ascertained. A remarkable point in their history results from this 

 power of feeding on flint. It is this : their bodies are indestructible. 

 Thus their constantly accumulating remains are gradually deposited 

 in strata, under the waters of the sea, as well as in lakes and ponds. 



* KalfB on British Desmidnse. London, 1818. Thirty-five coloiirod |)lntes. 



