58 



THE MECHANICAL FUNCTIONS. 



3,000 to 100,000 cells would be contained in an 

 extent of surface equal to a square inch. But they 

 are occasionally met with of different sizes, from 

 even the 1000th part of an inch to the 30th. 



In their original state, these vesicles have an 

 oval or globular form ; but they are soon transformed 

 into other shapes, either by the mutual compres- 

 sion which they sustain from being crowded into a 

 limited space, or from unequal expansions in the 

 progress of their developement. From the first of 

 these causes they often acquire angles, assuming the 

 forms of irregular rhomboidal dodecahedrons, and 

 often of hexagonal prisms, like the cells of a honey- 

 comb ; and by the second, they are elongated into 

 cylinders, or slowly tapering cones, thus passing 

 by insensible gradations into the tubular form. 

 Figures 6, 7, and 8, are representations of some of 

 these different states of transition from the one to 

 the other. These various modifications of the same 

 elementary texture have been distinguished into 



