VIII 



THE SEGMENTATION OF A DISC 



593 



aggregate of living cells than had the diagram of a, with whi«h we 

 began. 



Just as we have constructed in this case a series of purely 

 diagrammatic or schematic figures, so will it be possible as a rule 

 to diagrammatise, with but little alteration, the complicated ap- 

 pearances presented by any ordinary aggregate of cells. The 

 accompanying httle figure (Fig. 240), of a germinating 

 spore of a Liverwort (Riccia), after a drawing of D. H. 

 Campbell's, scarcely needs further explanation: for it is 

 well-nigh a typical diagram of the method of space- 

 partitioning which we are now considering. The same is 

 equally true of any one of Hanstein's figures of the 

 hairs on a leaf-bud*, or Berthold's of the small discoid algae. Let 

 us look again at our figures of Erythrotrichia or Chaetopeltis from 

 Berthold's Monograph, and redraw some of the earher stages. 



Ficr. 240. 



Fig. 241. Embryo-stages of Chaetopeltis orbicularis. After Berthold. 



In the following diagrams (Fig. 242) the new partitions, or those just 

 about to form, are in each case outhned ; and in the next succeeding 

 stage they are shewn after settling down into position, and after 

 exercising their respective tractions on the walls previously kid 

 down. It is clear, I think, that these four diagrammatic figures 

 represent all that is shewn in the first five stages drawn by Berthold 

 from the plant itself; ,but the correspondence cannot in this case 

 be precisely accurate, for the reason that Berthold's figures are 

 taken from different individuals, and so are not strictly and con- 

 secutively continuous. The last of the six drawings in Fig. 230 is 

 already too comphcated for diagrammatisation, that is to say it is 

 too comphcated for us to decipher with certainty the order of 

 appearance of the numerous partitions which it contains. But in 

 Fig. 243 I shew one more diagrammatic figure, of a disc which has 

 * Bot. Zeitung, xxvi, p. 11, xi, xii, 1868. 



