UNITIES OF LIFE 



the surface of the hollow sphere is called the blastoderm 

 (or germinal membrane). 



3. Arboreal Ccenobia. — The cell-community takes 

 the form of a small tree or shrub, the fixed cells secret- 

 ing jelly-like stalks at their base and these forming 

 branches. At the top of each stalk or branch is an in- 

 dependent cell; so in the case of the gomphonema and 

 many other diatomes, the codonocladium amoiig the 

 fiagellata, and the carchesium among the ciliata. 



4. Catenal Coenobia. — The cell-community forms a 

 chain, the links of which (the individual cells) are joined 

 in a row. We find chainlike cell-communities of this 

 sort, or "articulated threads," even among the monera 

 (oscillaria and nostic among the chromacea, leptothrix 

 among the bacteria). Among the diatomes we have the 

 bacillaria, among the thalamophora nodosaria, as ex- 

 amples. Many of the lower protophyta (algaria and 

 algetta) form the direct transition to the true algas 

 among the metaphyta, as the threadlike layer of the 

 latter (for instance, cladophora) is only a higher develop- 

 ment of the catenal coenobium, with polymorphism of 

 the co-ordinated cells. We may also regard these ar- 

 ticulated multicellular threads as the first sketch for the 

 formation of tissues in the metaphyta. 



The stable communities of cells which make up the 

 body of the histona, or multicellular plants and animals, 

 are called tissues (tela or hista). They differ from the 

 coenobia of the protists in that the social cells give up 

 their independence, assume different forms in the divi- 

 sion of labor, and subordinate themselves to the higher 

 unity of the organ. However, it would be just as diffi- 

 cult to lay down a sharp limit between the ccenobia and 

 the tissues as between the protists and the histona which 

 possess them; the latter have been developed phylo- 

 genetically from the former. The original physiological 

 independence of the cells which have combined to form 

 «i 161 



