INTRODUCTION. XXI 



amined these globules with the greatest care, and has convinced 

 himself of their oily nature. He regards them as representing 

 the amylaceous secretions of the Desmidiese and Confervse, and 

 the starch-granules of the cotyledons of the higher vegetables. 

 (Bacillarien, p. 23.) 



A distinct movement of the granular particles of the endo- 

 clirome, closely resembling the circulation of the cell-contents in 

 Closteriimi Lunula, noticed by Mr. Ralfs (British Desmidieae, Pre- 

 face, p. xxi.), and which I have frequently detected in the same 

 species, has occasionally fallen under my notice in some of the 

 larger species of Diatomaceas. 



In Surirella biseriata, Plate VIII. fig. 57, this motion has 

 been more especially apparent ; but I have also observed it take 

 place in NitzscMa scalaris, Plate XIV. fig. 115, and Campi/lo- 

 (liscus spiralis, Plate VII. fig. 54. 



This circulation has not, however, the regularity of move- 

 ment so conspicuous in the Desmidiese, and is of too am- 

 biguous a character to furnish data for any very certain conclu- 

 sions, save one, viz. that the Diatom must be a single cell, and 

 cannot contain a number of separate organs, such as have been 

 alleged to occupy its interior; since the endochrome moves 

 freely from one portion of the frustule to another, approaching 

 and receding from the central nucleus unimpeded by any inter- 

 vening obstacle. 



Of the chemical composition of the endochrome, I am at pre- 

 sent unable to offer a satisfactory analysis. Professor Prankland, 

 of Manchester, who kindly consented to direct his attention to 

 the chemical constituents of these organisms, but whose engage- 

 ments have hitherto prevented him from completing the neces- 

 sary investigations, informs me that a large amount of Kon exists 

 in the state of a silicate or protoxide in the siliceous epiderm ; 

 and he attributes to its presence the brown colom* which is 

 assumed upon exposing the Diatoms to the influence of a 

 moderate heat, the protoxide of iron, by the gradual absorption 

 of oxygen, being converted into brown peroxide of iron, which 

 assumes a redder tinge upon being more strongly heated. 



Of the behaviour of the endochrome under the influence of 

 certain reagents, I may merely remark at present, that dilute 



