OF MICROSCOPIC OBJECTS. 09 - 
sometimes around which, is a mass of viscid matter called 
the “ endochrome.” ‘They are found in almost every descrip- 
tion of water, according to the variety: some prefer sea- 
water, others fresh, and many are seen nowhere but in that 
which is a mixture of both, as the mouths of rivers, &c. 
Ditches, ponds, cisterns, and indeed almost every reservoir, 
yield abundance of these forms, They are not, however, 
confined to “present” life; but, owing to the almost in- 
destructible nature of their siliceous covering, they are 
found in a fossil state in certain earths in great abundance, — 
and are often termed “ fossil Infasoria.” Upon these frus- 
tules are generally to be seen lines, or markings, of 
different degrees of minuteness, the delicacy of which often 
serves the purpose of testing the defining power of object- 
glasses. Some of the frustules are triangular, others circular, 
and, indeed, of almost every conceivable shape, many of 
them presenting us with exquisitely beautiful designs. 
The markings, however, are seldom seen well, if at all, 
until the frustules are properly prepared, the different 
methods of accomplishing which will be given a little 
farther on. 
- The collection of fresh diatoms is so closely connected 
with their preservation, that a few notes may be given upon 
it before we pass on. For this purpose a number of small 
bottles must be provided, which may be placed in a tin box, 
with a separate compartment for each, so that all chance of 
breakage may be done away with. The diatoms are generally 
of a light brown colour; and where they are observed in the 
water, the bottle may be so placed, with the mouth closed 
by the finger, that when the finger is withdrawn the water 
will rush in, carrying the diatoms also. If they are seen 
upon plants, stones, or any other substance, they may 
generally be detached and placed in the bottle. When 
there is a green covering upon the surface of the water, a 
great quantity of diatoms is usually found amongst it; as 
also upon the surface of the mud in those ponds where they 
abound, In these cases, a broad flat spoon will be found 
