544 THE NATURAL HISTORY OF 



a. Either, the zoospore does not develop, during the 

 period of its motility, any rigid, tough, ligneous lueai- 

 brane, but only when the motility has ceased, whereupon 

 the zoospore passes into the still form. This is the case 

 in the peculiar naked zoospores, of minute size, which are 

 produced in greater number than 2, that is to say, to the 

 number of 8, 16, 32, 64, from the parent-cell. They 

 cannot multiply until they have assumed the still 

 form : 



b. Or, the zoospore, during the period of its motility, 

 acquires a delicate but rigid membrane, which, however, 

 is separated from the primordial cell by an aqueous fluid ; 

 it then represents the encysted zoospore. These are 

 capable of propagation by segmentation, reproducing, 

 however, only motile forms, although sometimes non- 

 equivalent ones. 



Besides this, the primordial cell in the encysted 

 zoospore may produce a second, rigid, tough, ligneous 

 membrane, around its whole periphery, by which it is 

 closely surrounded, whilst the delicate, outer enveloping 

 cell is removed. In this way the encysted zoospores ])ass 

 into the still form, and the cycle of possible developmental 

 forms is closed. 



These appear to be the essential laws to which all the 

 phenomena attending the development of Protococcvs 

 pluvialis may be referred ; and the author then proceeds 

 to particular instances. 



It is difficult, from the numerous uninterrupted links 

 of a chain of phenomena, to select that which should be 

 regarded as the representative of the normal condition, 

 and to which all the rest might be referred ; but, on 

 the other hand, it is indifferent where the commence- 

 ment is made, and the author therefore commences with 

 the still form, which, within a rigid, tolerably thick, 

 ligneous membrane, indicated by a double contour 

 line, contains uniformly red, opaque, granular contents, 

 contractile in alcohol, and presenting in the centre 

 a cytoblast (?) in the form of a hghter coloured vesicle 



