1870 J OSLER — ON CANADIAJf DIATOMACE^. 14^ 



motion beiu'g a special characteristic of animal life, claimed for 

 tliem a place wfth the former ; stricter investigations, aided with 

 better instruments, have proved most conclusively that their real 

 position is among the Protophytae. 



A Diatom consists, essentially, of a single cell, and only differs 

 from the other unicellular plants in the ultimate structure of its 

 cell wall, which is impregnated with silex — this impregnation 

 always following a definite and distinct pattern in each organism, ■ 

 and forming a most valuable means of determining the species. — 

 I need hardly observe that this secretion of silex is by no means 

 peculiar to the Diatomaceie ; parallel instances are found in the 

 Equisteas, and many other plants. On examining a living frustule 

 the cell-contents are clearly seen, consisting of a bright central 

 nucleus (not always visible,) and a yellowish brown-coloured sub- 

 stance called Endochrome, dispersed throughout the frustule; 

 this is sometimes seen to exhibit the phenomenon of cyclosis, 

 moving freely from one portion of the cell to the other. In 

 addition, several oil-globules are usually present. These, at 

 certain seasons, become very abundant ; so much so, as almost 

 to take the place of the Endochrome. At the apices and sides 

 of the frustule a clear or slightly granular substance exists, which, 

 as we shall see, Prof. Schultze believes to be the chief ao-ent in 

 producing the movements of this family. A curious motion of 

 granules is to be observed in some diatoms, which is very similar 

 to, and probably owes it origin to the same cause as the " swarm- 

 ing of the Desmids." 



The siliceous envelope is composed of two valves of the most 

 perfect symmetry, which are at first in close proximity to one 

 another, and enclose between them the cell-contents; but as the 

 process of self division goes on, the valves separate from each 

 other, and a hoop or connecting membrane is formed, usually con- 

 taining less silex, and not often presenting the beautiful markings 

 so well seen on the valves. The connecting membrane generally 

 separates from the valve on the application of strong heat, or on 

 boiling the frustules with nitric acid. 



When the connecting membrane is turned towards the observer, 

 it is said to be the "front view; " when the valves are turned, 

 the " side view." It is on the valves principally that the mark- 

 ings so characteristic of the Diatoniacea3, and about which so much 

 discussion has taken place, occur. Until recently, great uncer- 

 tainty prevailed as to the true nature of these markings, especially 



