33 o SCIENCE PROGRESS. 



the fissiparous bipartitions of the protoplastids, and the suc- 

 cessive cellular divisions in the developing metaplastid 

 embryo, are brought about by complex nuclear metamor- 

 phoses in a similar way. Roughly speaking, therefore, and 

 with certain reservations, of which I shall speak immediately, 

 there appears to be an essential similarity between the pro- 

 cess of cellular multiplication, by which the single complex 

 individuality of a metaplastid is built up, and the fissiparous 

 multiplication of independent protoplastid organisms. In 

 the little green plant Pandoriua, the fertilised ovum gives 

 rise, by division, to three or four separate cells or proto- 

 plastid individuals, which, in turn, produce each sixteen 

 daughter elements, and these do not separate from one 

 another, but remain compounded into distinct metaplastid 

 individuals with sixteen cells. After further multiplication 

 of the cells of each of these individuals, the whole of the 

 histological elements produced, separate from one another, 

 and assume once more the form of true flagellate proto- 

 plastids, among which conjugation may occur, and the whole 

 process is repeated. 



Thus the development of a form like Pandorina is a 

 process similar in its fundamental features to the life cycle of 

 the protoplastid forms, and although, during the evolution, 

 certain new characters are added to the fundamental and 

 similar groundwork, by the formation of three or four 

 metaplastid individuals, these apparently new characters may 

 in reality be nothing more than a modification of the correla- 

 tion existing among the individuals of a colony of proto- 

 plasts. Further, in a case like Pandorina, every cell of 

 which the metaplastid is composed can, and usually does, 

 give rise to more or fewer flagellate individuals, which after 

 conjugation repeat the life cycle over again ; but in many 

 of the higher plants, and in all the metozoa, this capacity 

 of every histological element to reproduce the parent species 

 has been lost, and in most cases the faculty or power 

 of the vast majority of the cells composing a metaplastid 

 body, to return even to a flagellate or protoplastid form 

 like the conjugating gametes of algae has vanished also. 

 The relegation of this power to certain tracts or repro- 



