FRESH- WATER ALGA. ant 
should be boiled with strong nitric acid, and care- 
fully and repeatedly washed. Some species con- 
sist of chains of parallelograms (Fig. 24), connected 
together at one single point, more beautiful in ap- 
Fic. 24.—DI1ATOMA BIDDULPHIANA—magnified. 
pearance, and more richly and elaborately carved 
than the costliest bracelet on the arm of a queen. 
Some resemble miniature 
flags or fans, adorned with 
the most exquisite figures ; 
some graceful boats, frost- 
edand granulated, in which 
a tiny animalcule might 
float over a dew-drop; and 
some little trees (Fig. 25), 
covered with variegated 
leaves, arranged in fan- 
like clusters, as though 
intended for microscopic 
Fic 25.—EXILARIA FLABELLATA. models of a grove of fan- 
palms. In short, they form circles, triangles, 
squares, and almost every kind of mathematical 
figure (Fig. 26), to the utter subversion of all the 
