136 JOURNAL OF THE [December, 



even these infinitesimals have their life activities and phe- 

 nomena. 



Of such an atomy it falls to us to narrate, as best we may, the 

 life-history. 



First, then, what does the name Diatom denote ? Literally, 

 it means something cut through at even distances. The word 

 was coined by the earlier naturalists, whose studies of these 

 organisms seem to have been confined to those species which in 

 the living state are found in series like a chain, broken nearly 

 across in clean fractures, as if cut, at uniform distances along 

 the chain. Sometimes they were called "brittleworts." This 

 chain-like feature is shown in the species Diatoma vulgare. 

 But as this peculiar habit is true of a very few species only, the 

 name, Diatoms, given to these organisms, was not well chosen. 



Second. Let us now look at the general form, or, rather, the 

 typical structure of a diatom; for the variety of forms is very great. 

 Indeed, in the production of this vast group, the Diatomaceae, 

 and its allied order the Desmidiacese, Nature seems to have set 

 herself the task of showing how many symmetrical-geometrical 

 forms she could devise between a straight line and a circle — 

 between the hair-like Nitzschia, on the one hand, and the gor- 

 geous Arachnoidiscus, a discoidal, circular-box-shaped diatom, 

 on the other. There are forms quadrate, oblong, rhomboidal, 

 triangular, arcuate, ellipsoidal, ovate, spiral. These may be set 

 down as geometrical. Then there are shapes which bear more 

 or less resemblance to well-known objects, as spatulas, boats, 

 stars, bottles {^Amphorce), crosses, etc.; and many of the diatoms, 

 surprising to add, are sculptured with designs too delicate, too 

 ornate, for pencil to delineate or words to describe. Through- 

 out this multiplicity of forms the family likeness is never en- 

 tirely lost. The ordinary systematist can in every instance 

 recognize the diatom. 



As to the skeletal structure of a diatom : For illustration, 

 here is a little oblong chest. You will notice that the lower 

 part has a flange over which the upper part shuts. The interior 

 has no compartments. Let us be a little technical, and instead 

 of calling this a box, call it a cell. Now, suppose it to be 

 covered with morocco, like my lady's jewel-case. This covering 

 must be called a membrane, or epidermis. What is wood in 

 our little casket is, in the diatom, silica. I do not state that I 



