PltOTOCOCCUS PLUVIALIS. 541 



rocephalus. It is in the form of extraordinarily minute 

 (from 0'0015'" to 0-004'") globules, consisting of a green, 

 red, and colourless substance (protoplasm) in unequal 

 proportions. The colourless protoplasm, in these, as in all 

 primordial cells, constitutes the outermost delicate boun- 

 dary; the red substance is for the most part agglome- 

 rated towards the anterior end in minute spherules, the 

 granular green substance occupies more the under part, 

 whilst the middle is most usually colourless. The shape 

 varies extremely. 



Hence it is apparent that the naked zoospores, although 

 as regards their development not of equal value, are all 

 constructed in an analogous manner, varying only in 

 their mutable form, size, and colour. But they are all 

 true primordial cells, which before desiccation undergo 

 deliquescence, having no rigid, solid, ligneous membrane, 

 being enveloped only in a mutable layer of protoplasm, 

 and with colourless green and red contents, in part 

 organised into granules and droplets, rarely containing 

 colourless granules of unknown nature, and chlorophyll 

 vesicles, and always moved by means of two longer or 

 shorter vibratile filaments. 



Having thus gone over the anatomical description of 

 the various forms of Protococcus, the author proceeds to 

 the history of its development. 



1. The Protococcus pluvialis is a unicellular Alga, a 

 simple cell, or at least the individual represents an 

 organism which exhibits the conditions of a simple cell ; 

 each multiplication of the cell reproduces the species, and 

 is at the same time an act of propagation ; each dissolu- 

 tion of the parent-cell into secondary ones constitutes a 

 new generation ; each secondary cell is an independent 

 individual of the same species. 



2. The Protococcus pluvialis is a plant subject to an 

 " alternation of generations j" that is to say, the com- 

 plete idea of the species is not exhibited in it until after a 

 series of generations. The forms of development which can 

 be possibly comprehended in the idea of the species, do not 



