vm]« OR CELL-AGGREGATES 643 



margin of the cell. The phenomenon is precisely identical to that 

 bisection of a quadrant by means of a circular arc, of which we 

 spoke on p. 581, and the annular film is very easy to reproduce 

 by means of a soap-bubble in the bottom of a cyUndrical dish or 

 beaker. The next partition is a perichnal one, concentric with the 

 outer surface of the young antheridium ; and this in turn is followed 

 by a concave partition which cuts off the apex of the original cell : 

 but which becomes connected with the second, or perichnal partition 

 in precisely the same annular fashion as the first partition did with 

 the base of the httle antheridium. The result is that, at this stage, 

 we have four cell-cavities in the little antheridium- (1) a central 



Fig. 291. Development of anthe- 



11- c,n,. o ^- ^L L r J r ridium of Pteris. After Stras- 



J^ig. 290. Section through frond of 



Girardia sphacelaria. After Goebel. ^ 



cavity; (2) an annular space around the lower margin; (3) a narrow 

 annular or cylindrical space around the sides of the antheridium; 

 and (4) a small terminal or apical cell. It is evident that the 

 tendency, in the next place, will be to subdivide the flattened 

 external cells by means of anticlinal partitions, and so to convert 

 the whole structure into a single layer of epidermal cells, surrounding 

 a central cell within which, in course of time, the antherozoids are 

 developed. 



The foregoing account deals only with a few elementary pheno- 

 mena, and may seem to fall far short of an attempt to deal in general 

 with "the forms of tissues." But it is the principle involved, and 

 not its ultimate and very complex results, that we can alone attempt 

 to grapple with. The stock-in-trade of mathematical physics, in 

 all the subjects with which that science "deals, is for the most part 



