46 THE INTERNAL 



In the nutrition and growth of the cell-wall, two 

 conditions may be distinguished. The growth, namely, 

 may be solely confined to the alteration and enlargement 

 of the boundaries of the cell. Hence, very various forms 

 gradually arise out of the originally roundish cells. In the 

 next place when they become crowded closely together, 

 they lose their roundly protruded shape, press each other 

 flat, and then appear like very irregular honey-comb cells 

 or, in a delicate cross section, like many-sided meshes, 

 (PL I, Fig. 13, a.) Other cells take a stellate figure in 

 their expansion, and form elongated processes which 

 sometimes convert them into elegant six-rayed stars, 

 and as often give them very irregular and curious shapes. 

 Others again become flattened by pressure on two opposite 

 sides, and, finally, others become elongated and assume 

 the appearance of cylinders, prisms, &c., or when still 

 more stretched out, are found spindle-shaped or in the 

 form of long, thin filaments, (PL i, Figs. 6, 7, 8, and 

 13, 5.) 



Throughout all these changes of form, the wall of the 

 cell may retain its original thickness ; it always remains 

 closed and perfectly entire. But a second change generally 

 occurs, the thickening of the wall. The way in which 

 this is produced, is by the deposition of a new layer upon 

 the inside of the original cell-wall, between it and the 

 primordial utricle. There are some peculiarities in this 

 process ; the new layer is never a similar perfectly entire 

 membrane, but seems broken up in a great variety of 

 different ways. Sometimes it is perforated all over with 

 little chinks, (PL I, Fig. 6 ; PL n, Fig. 8, &,) at others 

 with longer slits, (PL i, Fig. 4,) now it appears like 

 a net-work, now it is completely cut up into a spirally- 

 wound band, (PL i, Fig. 5,) and in another case it exhibits 



