584 



THE FORMS OF TISSUES 



[CH, 



yet how the triangular portion ought to divide; but it is obvious 

 that the least possible partition-wall which shall bisect the other 

 must run across the long axis of the oblong, that is to say periclihally. 

 This is precisely what tends actually to take place. In the following 

 diagrams (Fig. 234) of a frog's egg dividing under pressure, that 

 is to say when reduced to the form of a flattened plate, we see, 

 firstly (A), the division into four quadrants (by the partitions L 2); 

 secondly (B), the division of each quadrant by means of an anti- 

 clinal circular arc (3, 3), cutting the peripheral wall of the quaarant 

 approximately in the proportions of three to seven; and thirdly 



3 



ABO 

 Fig. 234. Segmentation of frog's egg, under artificial compression. 

 After Roux. 



(C), we see that of the eight cells (four triangular and four oblong) 

 into which the whole egg is now divided, the four which we have 

 called oblong now proceed to divide by partitions transverse to 

 their long axes, or roughly parallel to' the periphery of the egg. 



The question how the other, or triangular, portion of the divided 

 quadrant will next divide leads us to a well-defined problem which 

 is only a shght extension, making allowance for the circular arcs, 

 of that elementary problem of the triangle we have already con- 

 sidered. We know now that an entire quadrant (in order that its 

 bisecting wall shall have the least possible area) must divide by 

 means of an antichnal partition, but how about any smaller sectors 

 of circles? It is obvious in the case of a small prismatic sector, 

 such as that shewn in Fig. 235, that a periclinal partition is the 

 least by which we can bisect the cell; we want, accordingly, to 

 know the limits below which the periclinal partition is always the 



