38 FORMS OF CELLS. 
almost, or entirely, free from pressure. But, under other cir- 
cumstances, in consequence of the mutual pressure of surround- 
ing cells, they assume a polygonal form (figs. 64 and 65), the 
number of the angles depending upon the number and arrange- 
ment of the contiguous cells. Thus, in a perfectly regular ar- 
rangement, when the contiguous cells are of equal size, we have 
dodecahedral cells, presenting, when cut transversely, an hexa- 
gonal appearance (jig. 66). Itis rarely, however, that we find 
Fic. 62. Fic. 65. Fia. 64, Fia, 65. 
Fig. 62. Rounded cells.——Fig. 63. Elliptic or ob'ong cell.—Figs. 64, 65. 
Polygonal cells in combination : those of the latter figure being pitted, 
cells of this regular form, since, in consequence of the unequal 
size of the contiguous cells, the polygons which result from their 
mutual pressure must be mcre or less irregular, and exhibit a 
variable number of sides (generally from three to eight). 
Secondly, when the growth is nearly uniform on all sides of 
the cell-wall, but not equally so at all points of its surface, we 
have cells which maintain a rounded form in the centre, but 
having rays projecting from them in various directions, by which 
they acquire a more or less star-like appearance (jigs. 67 and 
Fic. 66. Fic. 67. 
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Fig. 67. Stellate cells. 
Fig. 66. Transverse section of regular polygonal cells. 
93) ; and hence such cells are called stellate. These rays may be 
situated in one plane, or project from all sides of the cell. Itis 
rarely the case that such cells have the rays at regular intervals, 
or all of one length, but various degrees of irregularity occur, 
which lead to corresponding irregular forms in such cells. 
Thirdly, when the growth takes place chiefly in one direction, 
we have cells which are elongated, either horizontally or verti- 
