r.v \. mi IAD EDWARDS. L9 



objects in saoh a manner as to preserve them for almost any 

 length of time, and at the same time exhibit their characters to 



the best advantage, and although we have in the English lan- 

 guage at least three books treating specially of this subjec 

 the preparation of microscopic objects, yet hardly any one of 

 these volumes gives any concise, practical, and at the Bame 

 time, reliable descriptions of the best methods of collecting, 

 preparing and mouuting specimens of diatomacesB. In bo 

 generally, when the preparation of these organisms is tre 

 of, it is usually the fossil deposits which are considered, and 

 even such directions as relate to these are for the most part 

 meagre and unsatisfactory; and, when the specific and special 

 directions are, as is often the case, copied from one book into 

 the other without having been tested by the copyist, any faults 

 they may have possessed, as originally written, are merely re- 

 peated and not eliminated. To prepare and mount specimens 

 of diatomacea3, for the purpose of sale alone, is one thing, and 

 to prepare and mount them, so as to preserve and exhibit their 

 natural characters and fit them as objects of scientific study, is 

 another and very different thing. The latter can only be at- 

 tained after considerable practice, and to do it properly a con- 

 siderable amount of knowledge of their natural history is 

 plainly necessary. 



The diatomacea) should always be prepared and put up for a 

 special purpose, — that of exhibiting characters peculiar to 

 genera and species; and to do this those characters must of 

 course be known. Muds, guanos, dredgings. and gatherings of 

 that description, can seldom be used for the purpose of exhibit- 

 ing such characters, and when they can. in exceptional Cf 

 be so employed, it is when the forms they contain are Bel< 

 out in the manner to be described hereafter. Gatherings, like- 

 wise, which contain many Bpecies in a mixed condition, should, 

 as a general thing, be rejected unless there be present - 

 thing of special importance, such as rare sp< cries, or some large 

 and fine or distorted forms of common Bpeoii . B I eveD in 



such cases it will be found best not to mount the gatheriii: 

 collected, but to Beleoi out the forms desired and place them 

 14)011 slides by tmiiis. Ives, ami in such media as will exhibit 

 their peculiarities to the best advantage. Of course it may be 



