76 Elementary Biology. 



CHAPTER VII. 



METAPHYTA NON-VASCULARIA. 



SECTION I. FRESH-WATER Ki&fc 



IN the two preceding chapters we have discussed the struc- 

 ture and life-history of a representative of each of the two 

 groups known as Protophyta and Protozoa, or unicellular 

 plants and unicellular animals. We have seen, moreover, 

 that at one stage in the life-history of the example taken to 

 illustrate the Protophyta it assumed a temporary resem- 

 blance to a very elementary metaphyte. Protococcus was 

 found to divide into three or four pieces, which for a short 

 space of time remained attached to each other, forming a 

 very simple multicellular organism. It is to be noted, how- 

 ever, that the cells are really physiologically independent of 

 each other, being rather members of a colony than units in 

 one whole. The organism at this stage does not exhibit 

 that division of labour which has been already explained (at 

 page 37) as being characteristic of multicellular organisms, 

 It is quite true that many multicellular plants and animals 

 do show only a very slight approach to morphological 

 differentiation ; and we cannot be surprised that it is so, 

 since manifestly in the simplest beginnings of a metaphyte, 

 morphological sameness must precede differentiation. Every 

 plant and every animal has its cells at first perfectly similar. 

 It is only after a period, varying in duration with the nature 

 of the plani or the animal in question, that the cells begin 

 to be differentiated and become specially modified for the 

 performance of their several duties. 



