32 THE AMERICAN MONTHLY [Febrnaiy, 



The following are the advantages of tlie apparatus : 



1. A constant flow of fresh water, which may be regulated by the 

 linen strip in the siphon. The water, while running, keeps saturated 

 with oxygen by means of the linen strip extending from the mouth of 

 the longer arm of the siphon. This strip also acts as a filter, retaining 

 any particles of dust that may have accumulated in the reservoir. 



2. The height of the capillary space between the cover-glass and the 

 slide being only of the thickness of an ordinary cover-glass, all objects 

 may easily be seen with an immersion lens. 



3. The immersion fluid may be removed from tlic cover-glass with- 

 out disturbing the objects. 



Interesting Items on Diatoms.* 



By CHAS. F. cox. 



NEW YORK. 



Assorting. — If we take the product of our filter and place dip- 

 pings from it under the microscope, we shall at first experience some 

 embarassment because of the multiplicity of objects presented to our 

 view. There will be an abundance of sand and other amorphous and 

 inorganic substances, and amongst these are likely to be scattered frag- 

 ments of leaves and stems of exogenous plants, bits of linen, cotton or 

 woollen threads, and various other articles of extraneous origin. 

 Prominent, however, because of their bright color and considerable 

 size, will appear the long-jointed tubes of a few of the thread-like 

 aquatic weeds, while deep down through the film of water we shall 

 discern two similar and yet somewhat diflerent sorts of diminutive 

 bodies, which are sure to fasten our attention by their very pretty and 

 symmetrical forms. The one kind is of a deep green color, the other 

 of a thin reddish or brownish-olive hue; and both will exhibit some 

 diflerencing of their internal substance into denser and more attenuated 

 parts, with here and there open, oily-looking spots. The dark green 

 bodies appear as single capsules, narrowed, if not pointed, at each end, 

 and floating free or else as loose aggregations of similar flattened cells, 

 forming either rosettes or lace-like mats of various patterns. The 

 brownish bodies will be found either as nari'ow rods, laid side by side 

 in long bands, or joined to one another by their corners so as to form 

 zigzag lines, or else as disconnected individuals with a very striking 

 resemblance in shape to miniature skiffs or boats. If we make use ot 

 some other source of supply than our Croton-water faucet, we may ob- 

 tain a much greater variety of forms in both the classes of objects 

 referred to, though w^e shall not fail to notice a certain parallelism in 

 the morphology of the two families, wdiich may easily cause us to 

 think them but one. They are. however, quite distinct, as we shall 

 see. These forms which I have spoken of in this particular case as 

 decidedly green in color (although this is not a decisive characteristic 

 throughout the family) are known as Desmids. Those which I have 

 described as being of a brownish hue are Diatoms. 



Distinction between Desmids and Diatoms. — But now, if we 

 look more closely at our desmids and diatoms, we shall discover that 

 the latter have a very rigid, hard, and almost indestructible carapace or 

 shell, while that of the former is hardly more than a stiffened membrane 



* Paragraphs extracted from an address by Chas. F. Cox, and entitled, "What is a Diatom?" deliv- 

 ered December 18, 1891, before the New York Microscopical Society and published in the Society's 

 journal for January, 1892. 



