CIRCULATORY TISSUES, GENERAL Itf 



alone in Figure 131, D, but are combined with the circulation in Figure 

 133, F. The clumsiness and especially the lack of possible differentia- 

 tion of function in the separate invaginations in Figure 131, D, are done 

 away with by the circulation of Figure 132, , as applied in Figure 133, 

 F. One should now use the imagination and realize the fact that this 

 arrangement can be enlarged to almost any degree of complexity and 

 adapted to almost any need. A large number of different sorts of work 

 can be done in the different invaginated regions, and by the extension 



FIG. 133, F. Large mass of cells with perfect circulatory system and sufficient surface. 



and formation of new loops and branches of the circulatory channels the 

 products of these activities can be carried to any part of the organism 

 where they may be needed, or, if not needed, to any part of the body 

 where it is possible to get rid of them. 



The Figures 130 to 133 are diagrammatically correct as to relations of 

 surface to bulk and to thickness of cell layers. In each case the source 

 of surface supply is indicated by different formal shadings of the cells. 

 The blood channels shown in Figures 132 and 133 are the same, and 

 the invaginations are the same in Figure 131, D, and Figure 133, jp, 

 with the exception that the smallest invagination in Figure 131, D, is 

 omitted from Figure 133, F, to indicate the possibility of a region re- 

 mote from the surface, in a body supplied with a circulation. To pre- 

 serve the same value of surface, however, the place of this smallest 



