92 



AQUATIC MICROSCOPY FOR BEGINNERS. 



Fig. 64. — Bacilldria, 



3. .BACiLL>5.RrA, (Fig, 64). 



Frustules long and narrow, united laterally, freely 

 and rapidly sliding backward and forward over one 

 another; colony free-swimming- (Fig. 64). 



This is probably one of the most interesting of the 

 common fresh-water diatoms, on account of its 

 strange movements. 

 When quiet, as it prob- 

 ably will be immediatly 

 after being placed on the 

 slide, the band will some- 

 what resemble a row of 

 fence-pickets lying in 



contact side by side. Suddenly each picket shoots 

 forward until they all are nearly end to end, the band 

 becoming a long irregular line, when they quite as 

 suddenly close together again. This alternate back- 

 ward and forward gliding is continued until the 

 diatoms become apparently exhausted, or the oxygen 

 in the water is consumed. What prevents one 

 frustule from slipping off the end of the other is not 

 known;' indeed the cause of the entire frantic perform- 

 ance can .only be guessed at.* All the species of the 

 genus Bacillaria are said to live in salt or in brackish 

 water, but the form which I have 

 ventured to identify as a sweet- 

 water variety of B. paraddxa is 

 not uncommon in fresh-water ponds. 



. . . . , - Fjg. 65 and 650. — Fi ag- 



in my vicmity.in New Jersey. iUfia capudna. 



4. FragilAria CAPUcfNA (Figs. 65 and 65/7). 



Frustules very narrow, never wedge-shaped, band 

 long Fig. 65 shows the ribbon of united frustules; 



