A Treatise 



ON 



The Diatomace.e. 



INTRODUCTION. 



CHAPTER I. 



The Structure, Life History, Study, Collecting and 



Preparation of Diatoms. 



i. The Structure and Life History of Diatoms. 



i. Structure of Diatoms. Diatoms are microscopical algae. Each 

 individual diatom (called a frustule) consists of a single membranous cell, 

 enclosing, in addition to the liquid of the cell, a nucleus surrounded by 

 protoplasm, some oil globules, and a brownish matter called endochrome, which 

 is composed of chlorophyl and phycoxanthin. 



This cell is enclosed in a silicious covering or carapace, generally 

 forming a kind of box, and consisting of (A) two valves and (B) a zone 

 or connecting band, sometimes called a ringulum or girdle. 



According to the assertions now completely established of Messrs. 

 Wallich and Pfitzer, the two valves have each a rim, which overlaps 

 like the two parts of a pill-box. These two rims form the connecting 

 band, or the two rings of the girdle according to Prof. Pfitzer. 



The two connecting parts are independent and not united to the valves ? 

 as some authors allege. 



This independence of the connecting parts is now conclusively proved 

 by the beautiful section of a Navicula Dactylus made by Mr. W. Prinz 

 an illustration of which will hereafter be given (Chap. II. 3. Raphe 

 and nodules), and also by the same microscopist's successful sections of 

 Coscinodiscus, which we have carefully examined. 



B 



