96 THE SCIENCE OF LIFE. 



enlarge, break forth, but the silicious hoop which joined 

 the new frustules to the old one remains attached for a 

 time round one of them, causing some to appear trunc- 

 ated instead of round. 



The genus Navicula is so called from its resemblance 

 to a boat or little ship, (naus, a ship.) They are found 

 both living and in a fossil state. Some are striped lon- 

 gitudinally, and some transversely ; some are shaped like 

 an old-fashioned letter S, as the Pleurosigma, in which 

 the striae are resolved by a highly magnifying power into 

 hexagonal dots. 



10. In the Protophytes we see the endowments of 

 simple vegetable cells. A piece of bioplasm, or living 

 tissue, transforms its outer layer into cellulose, and 

 forms chlorophyll or starch in its interior, absorbing new 

 pabulum continually, and casting off the old effete atoms. 

 The relationship of each family is seen by these func- 

 tions common to all. Each species of each family has, 

 however, its own peculiarities, which distinguish it from 

 all others. The Protococci remain rounded cells, but 

 the Oscillatoria, Confervaceae, etc., have an instinct for 

 elongation, so that they become tubular, and for distrib- 

 uting endochrome in characteristic spiral patterns, vary- 

 ing in each species, while the Diatoms appropriate silica 

 from their pabulum to harden the cellulose envelope, 

 and arrange it in their frustules atom by atom, each 

 species after its own pattern, and all with marvelous 

 regularity and beauty. The Monistic theory of the 

 universe has no satisfactory reason to give for the exist- 

 ence of such varied tendencies. Schleiden has well said, 

 " We do, indeed, see into the mechanism of the puppet ; 



