FOOD OF THE OYSTER, CLAM, AND RIBBED MUSSEL. 385 



but the liou, devouring the cattle, depends as w ell ou the plants, since 

 without them the existence of his prey would be impossible. Exactly 

 the same thing takes place in the water; the tishes i)reying on other 

 hshes, these on smaller fishes, these again on other animals. All have 

 to come back hnally to animals living on plants. iSo 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 ligures. 

 The shells a and b separate as far as i)0ssible, so that one fits but 

 slightly over the other. A cross wall c 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 



-a^ 



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 tlie loss of size rpsulting from 

 this mode of division is compensated. 



A SIMPLE METHOD OF STAINING SMALL ORGANISMS. 



In the staining of unicellular algie, diatoms, and the reproductive 

 organs of the higher alga^, as well as many other micro-organisms, the 

 greatest ditHculty, as is well known, is encountered in the great loss of 

 specimens entailed by the more or less comi)licated 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 



