FOOD OF THE OYSTER, CLAM, AND RIBBED MUSSEL. 385 
4 
* 
but the lion, devouring the cattle, depends as well on the plants, since 
) without them the existence of his prey would be impossible. Exactly 
» the same thing takes place in the water; the fishes preying on other 
| fishes, these on smaller fishes, these again on other animals. Al have 
(to come back finally to animals living on plants. So we see that in the 
‘present case our oyster lives directly on plants, and there is no danger, 
‘as long as our waters contain the necessary salts for plants to live upon, 
that the food supply of the oyster will become exhausted, unless, indeed, 
(it should be found that in the embryonic stage the oyster depends upon 
‘some more precarious food supply. 
One subject of interest remains to be considered, namely, How do 
diatoms multiply? 
’ This is accomplished as represented in the accompanying figures. 
The shells a and b separate as far as possible, so that one fits but 
‘slightly over the other. A cross wall ¢ is now formed which splits into 
two, one of these forming the box for each of the two halves. It will 
be readily understood that in this way every daughter diatom is a little 
Vy 
[ie 
Ong ef 2) 
‘smaller than the mother, since the box of the mother now serves as 
‘the cover of the daughter. If this be repeated a certain number of 
(times, the diatoms would finally become too small for existence, but 
(then the small diatom leaves its shell and either simply grows, forming 
‘a new cell wall after a certain time, or it finds a mate, the bodies of 
| both merging into one, and in this way the loss of size resulting from 
\this mode of division is compensated. 
A SIMPLE METHOD OF STAINING SMALL ORGANISMS. 
In the staining of unicellular alge, diatoms, and the reproductive 
‘organs of the higher alg, as well as many other micro-organisins, the 
greatest difficulty, as is well known, is encountered in the great loss of 
specimens entailed by the more or less complicated staining process 
now in use. The one now commonly employed is as follows: The speci- 
men is hardened in a 1 per cent aqueous solution of chromic acid for 
twenty-four hours, washed carefully in water until the last trace of the 
acid is removed, then stained with a solution of carmine. It does not 
need to be pointed out that by the use of this method it is easy to lose 
the greater part of the organisms, and the disadvantages of it are 
F. R. 93 25 
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