14 



ORGANOGEAPHT. 



press ure of the surrounding organ s. We shall now allude to a 

 lew of tlie more common forms which cells assume. 



First, when the nutri tion is uniform , or nearly so, on all points 

 and sides of the cell^wall, we have a spherical or sligh tly ellip tic 



Fig. 17. Fig. 18. Fig. 19. Fig. 20. 



Fig. 21. 



Fig. 17. Rounded cells. 



Fig. 18. Elliptic or oblong cell. 



Figs. 19, 20,21. Polygonal cells. 



cell [fig. 17): when it is greater at the two extremities than at 

 the sides, the form is truly elliptic {fig. 18). In the above cases, 

 also, the cells are almost freen-om pressure. Under other cir- 

 cumstances, in co nseque nce of t he mutual pressure o f surround - 

 ing cells, they assume a pon/ao?iaC i'oim {Jigs. 19, 20, and 21), the 

 iiumLer of the angles depenciing upon the number and arrange- 

 ment of the contiguous cells. Thus, in a perfectly regular ar- 

 rangement, w hen the contiguous cells are of equal sizerwe have 

 dodccaJudral cells, presenting, when cut transversely, a hexa- 

 '^gonal appearance {fig. 21). It is rarely, however, that we find 

 cells of this regular mathematical form, since, in consequence of 

 the unequal size of the contiguous cells, the polygons which re- 

 sult from their mutual pressure must be more or 

 less irregular, and exhibit a variable number of 

 sides (generally from three to eight) fig. 20. 



Secondly, w hen the nu tr ition is nearly uniform 

 on all sides~of the cell-M'all, but not equally so at 

 all poruts~ of its^iTHa ce, we have cells w hich 

 maintain a somewhat rounded tornTin the centre, 

 but having rays projecting from them in various 

 Fig. 22. Stellate directions, by which they acquire a somewhat star- 

 cells, j-j^g appearance {fig. 22); and hence such c«lls 

 are calle d stellate . These rays may be situated in one plane, or 

 project from all' sides of the cell. It is rarely the case that 



Fig. 22. 



