Such masses are held together by a kind of sticky jelly, and if the hand is passed through it a very slight roughness may be perceptible, caused by the flinty diatom shells or cases.
Mere specks indeed they are, individually too minute to be seen by a human eye, unaided. Yet how marvellous in their make!
A Diatom plant or vegetable or sea-weed, whichever we choose to call it, is like a Foraminifer of the simplest possible structure. It consists of a single cell, with an outside flinty coating or inclosure, answering to the wood of a tree or the skeleton of an animal.
This flint casing, though infinitely small and delicate, is yet firm enough to prevent the passage of water through it; and also it is practically indestructible by ordinary forces. Diatom-cases, dropping to the ocean-bed, may lie there for ages.
DIATOM CASES (ARACHNOIDISCUS JAPONICUS)
Reproduced by permission of Messrs. R. and J. Beck, Ltd., and Messrs. J. and A. Churchill, publishers of Carpenter’s “The Microscope”
Face page 154
The living cell is inclosed in the said “case,” which is a kind of box, consisting of two halves or “frustules,” neatly joined together by a ring or girdle.
Diatoms increase in numbers, like many of the Foraminifera, by simply dividing into two. When the living cell thus parts, each half takes as its share one side of the box, and each then makes another side, or “frustule,” to complete itself. For this operation, the tiny ring or hoop doubles into a pair of hoops, one of which clings to each half of the case.