14 JOURNAL OF THE [January, 



mon sense somehow recognizes as belonging to the vegetable 

 kingdom, we arrive at a decision that the object of our considera- 

 tion is a plant and not an animal. 



This may not be a strictly scientific way of settling the ques. 

 tion, but how else are we to dispose of it when so great a stickler 

 for inductive methods, as Prof. Huxley, declares that the latest 

 information on this subject tends to the conclusion "that the 

 difference between animal and plant is one of degree, rather than 

 of kind; and that the problem whether, in a given case, an organ- 

 ism is an animal or a plant, may be essentially insoluble " ? 



Having made up our minds that diatoms lie within the bound- 

 aries of the vegetable kingdom, we shall have no difficulty in 

 referring them to that sub-kingdom which includes all non- 

 vascular, or, in other words, leafless and rootless plants, — called 

 thallophyia. In this sub-kingdom is the well-known class Algce, 

 which embraces all aquatic thallophytes, and to which therefore 

 the diatoms must belong. Indeed, they constitute a very impor- 

 tant sub-class of algae, which derives its name from them, — the 

 diatomacecB. 



The diatomaceje themselves get their name from the Greek 

 word 6iato}xo?, which means cut through, cut in two, or cut up, 

 and which was applied to them with reference to the bead-like 

 manner in which the individuals of many genera cling together 

 in fragile strings. These are the forms which earliest attracted 

 attention, and which in common language were described as 

 "brittle-worts," an appellation intended to connote the same 

 characteristic as is denoted by the Greek name. The latter 

 possesses additional appropriateness because of the fact that each 

 frustule is bivalvular in structure, and from the still further fact 

 that one of its modes of reproduction is a cutting in two of 

 every parent cell to form twin descendants. When this process 

 continues through several generations without an actual separa- 

 tion, the result is a loosely united filament, fillet, or flabel, accord- 

 ing to whether the parent form was round, square, or wedge- 

 shaped. The string, band, or fan thus produced will be cuti?ito 

 at regular intervals and may easily be cut up, or broken up, by 

 the application of any external force. 



Reproduction by self-division is not at all peculiar to this sub- 

 class, nor even to the vegetable kingdom. Animals, as well as 



