204 Transactions of the 



In fine, for useful purposes, in a small as well as large collec- 

 tion, it seems to me a moderate illustration of elementary tissues is 

 sufficient to be kept apart. These need not include inorganic sub- 

 stances, vegetable and animal components together in a series ; but 

 under each kingdom a few typical slides will convey all that is 

 wanted concerning the material which builds up organs, &c. As 

 to their proper position, they may precede, be dovetailed as a sub- 

 section in the midst, or terminate large groups. But I reiterate that 

 ostensibly to anyone fairly acquaint with structural morphology, 

 cellular, fibrous tissues, and such like, can nearly always find a 

 convenient corner along with the group of organs they help to 

 build up. 



The microscope rigidly defines the structures differentiating the 

 mineral, vegetable, and animal kingdoms ; these groups, practically 

 speaking, are thus sufficiently characteristic to form a groundwork 

 of classification. They therefore serve as primary natural divisions . 

 Proceeding from the simple to the more complex, the mineral king- 

 dom first engages attention. 



The classification of minerals and rocks is dependent either on 

 their chemical composition or the peculiar form of their crystal — 

 so micro- chemicals precede micro-minerals. In the structure of 

 chemical elements and compounds, or simple and complex mineral 

 substances, I am not aware of any gradation of minute form upon 

 which a microscopic classification could with propriety rest. The 

 subdivisions in either case therefore must be few, and follow con- 

 ventionally the recognized systems employed in text-books.* 



Amongst others, polarizing objects may form a convenient 

 subsection. When many specimens of a single substance obtain — 

 take, as a sample, coal sections — then a division geographically as 

 well as structurally is valuable. Especially in such a substance as 

 that mentioned is it legitimate, because there is no very clear 

 gradal series to classify them with texturally. I differ from those 

 who form a microscopic geology. Microzoal deposits or structures, 

 whatever their nature, truly belong to the series of micro-biological 

 specimens, if the term is applicable. 



Above all, it must be remembered that the variety of purpose 

 of a collection, its limited nature or miscellaneous character, render 

 equivalence or diversity in grouping convenient or otherwise. But 

 I would press my conviction, that there should always be appended to 

 each natural division a series illustrating application to the arts and 

 manufactures, whereby utility to every-day life, as it were, is recog- 

 nized ; and whereby comparison of objects as respects their purity 

 and genuineness can freely be tested. 



* I must not omit allusion to a paper by Mr. Davis Forbes, '' The Microscope 

 in Geology," 'Popular Science Review,' Oct., 18G7, whose classification I adopt in 

 my concluding section. 



