PROTOCOCCUS PLUVIALIS. 537 



starch, and larger colourless granules of unknown ma- 

 terial. 



The so ^termed " vacuoles" occur, in greater or less 

 number, in the interior of the primordial cells ; they must 

 be regarded as clear aqueous secretions from the colourless 

 or coloured protoplasm, which is consequently forced from 

 the centre of the cell towards the periphery. They are 

 formed, and change, both in number and figure, under 

 the eye of the observer, and present the aspect of large, 

 hollow, clear vesicles, which have the effect of causing 

 the coloured contents to appear frothy (Figs. 21, 27) ; and 

 they are frequently developed in such number, that the 

 coloured protoplasm seems only like a green deposit 

 on the wall, and even there to be wanting in parts. By 

 them it is that the internal watery cell-contents, as in the 

 common plant-cell, become definitely separated from tlie 

 more dense peripheric protoplasm (the primordial utricle). 

 The chlorophyll-vesicles resemble, in all respects, those 

 already described in speaking of the still form. They 

 are occasionally wanting in every form of cell, but gene- 

 rally so in the more minute, one or two-coloured pri- 

 mordial cells. (Fig. 41.) 



By starch granules are meant, in this case as in the 

 still cells, very minute, colourless, strongly refractive 

 particles or granules, rendered blue by iodine, and which, 

 on the first appearance of the contents, are present in 

 great abundance in certain stages. 



The colourless granules, which were met with only on 

 one occasion, in almost all the cells in the vessel, espe- 

 cially in the smallest, were highly refractive, spherical, 

 transparent corpuscles, visible through the coloured con- 

 tents. They were neither coloured nor changed by iodine, 

 acids, or alkalies. They resemble similar corpuscles 

 which occur in Uuglena viridis at certain times. 



The author then proceeds to describe the infinite 

 variety in appearance of different individual cells, owing 

 to the varying quantities or arrangement of the elements 

 above described ; almost the only part of a motile Pro- 



