CHAPTER XXV 



GENERAL PLAN OF MULTICELLULAR BEINGS 



MULTICELLULAR beings are constructed according to very 

 different types varying from the chestnut-tree to man, not 

 to speak of mushrooms and sea-urchins. Consequently it 

 is difficult to give a morphological plan common to all such 

 beings. In this chapter I have only to point out the conse- 

 quences of a fact, namely, that we are now considering as 

 entities by themselves, not cells, but agglomerations of cells. 

 Such an agglomeration has necessarily to be bounded by 

 a contour a surface separating it from the environment. 

 Whatever is comprised within this contour we call the body 

 of the multicellular being. But we have already seen that 

 its contents are very heterogeneous ; they comprise living 



cells (Fig. 7, P) and 

 Excretion intervals between living 



cells (Fig. 7, M). 



To all that fills the 

 total interval M of the 

 living cell we give the 

 name of interior 

 medium. 



Between this interior 

 medium and the cellu- 

 lar bodies P are pro- 

 FIG. 7. duced the exchanges 



154 



P-^i- 



Circulation 



