STRUCTURE OF PROTOCOCCUS 



543 



If this (as seems probable) constitutes the entire life-cycle of 

 r<ilniogloe-a, it affords no example of that curious 'motile' stage 

 which is exhibited by most algal protophytes in some stage of their 

 existence, ami which constitutes a large part of the life -history of 

 the minute unicellular organism now to be described. Protococdis 

 pluvialis, Ktz. (GJdamydococcus -plai-lnUs, A. Br.) (fig. 418), which 

 is not uncommon in collections of rain-water. Xot only has this 

 protophyte, in its motile condition, been very commonly regarded as 

 an animalcule, but its different states have been described under 

 several different names. In the first place, the colour of its cells 

 varies considerably ; since, although they are usually green at the 

 period of their most active life, they arc sometimes red; and their 

 red form has received the distinguishing appellation of Hwmato- 



FIG. 41s. Development of Protococcus pluvialis. 



commonl the red 



colouring matter 



forms only 



coccus. 



a central mass of greater or less size, having the appearance of 

 a nucleus (as shown at E. fig. 418); and sometimes it is reduced 

 to a single granular point, which has been described by Professor 

 Ehrenberg as the ci/<>-s]>c>t of these so-called animalcules. It is 

 quite certain that the red colouring substance is very nearly related 

 in its chemical character to the green, and that the one may be 

 converted into the other, though the conditions under which this 

 conversion takes place are not precisely known. In the 'still' form 

 of the cell, with which we may commence the history of its life, the 

 endoplasm consists of a colourless protoplasm, through which red or 

 green coloured granules are more or less uniformly diffused ; and 1 he 

 surface of the colourless protoplasm is condensed into an ectoplasm, 

 which is surrounded by a tolerably firm cell-wall, consisting of cellulose 



