6o THE HISTORY OF CREATION. 



Fig. 14. — Navicula hippocampus (greatly magnified). 

 In the middle of the cell the cell-kernel (nucleus) is 

 visible, together with its kernel speck (nucleolus). 



The Flint-cells (Diatom ese), a sixth class of 

 Protista, are perhaps the most closely related 

 to the Labyrinthulece. These primary crea- 

 tures — which at present are generally con- 

 sidered as plants, although some celebrated 

 naturalists stiU look upon them as animals — 

 inhabit the sea and fresh waters in immense 

 masses, and offer an endless variety of the 

 most elegant forms. They are mostly small microscopic 

 ceUs, which either live singly (Fig. 14), or united in great 

 numbers, and occur either attached to objects, or glide and 

 creep about in a peculiar manner. Their soft ceU-substance, 

 which is of a characteristic brownish yellow colour, is 

 always enclosed by a solid and hard flinty shell, possessing 

 the neatest and most varied forms. This flinty covering is 

 open to the exterior only by one or two slits, through 

 which the enclosed soft plasma-body communicates with 

 the outer world. The flinty cases are found petrified in 

 masses, and many rocks — for example, the Tripoli slate 

 polish, the Swedish mountain meal, etc., — are in a great 

 measure composed of them. 



A seventh class of Protista is formed by the remarkable 

 Slime-moulds (Myxomycetes). They were formerly uni- 

 versally considered as plants, as real Fungi, until ten years 

 ago the botanist De Bary, by discovering their ontogeny, 

 proved them to be quite distinct from Fungi, and rather 

 to be akin to the lower animals. The mature body is a 



