VIIl] 



THE SEGMENTATION OF A DISC 



367 



cosec 6 — cot 6 = OM, that is to say the distances from the centre, 

 along the side of the cell, of the starting-point (M) of the anticlinal 

 partition. The point C" represents its position in the case of 

 a quadrant, and shews it to be (as we have already said) about 

 3/10 of the length of the radius from the centre. If, on the other 

 hand, our cell be an equilateral triangle, then we have to read off 

 the point on this curve corresponding to a = 60°, and we find it 

 at the point F'" (vertically under F), which tells us that the 

 partition now starts 4-5/10, or nearly halfway, along the radial 

 wall. 



The foregoing considerations carry us a long way in our 

 investigations of many of the simpler forms of cell-division. 

 Strictly speaking they are limited to the case of flattened cells, 

 in which we can treat the problem as though we were simply 

 partitioning a plane surface. But it is obvious that, though they 

 do not teach us the whole conformation of the partition which 

 divides a more compUcated solid into two halves, yet they do, even 

 in such a case, enlighten us so far, that they tell us the appearance 

 presented in one plane of the actual solid. And as this is all that 

 we see in a microscopic section, it follows that the results we have 

 arrived at will greatly help us in the interpretation of microscopic 

 appearances, even in comparatively complex cases of cell-division. 



Let us now return to our 

 quadrant cell {OAPB), which we 

 have found to be divided into 

 a triangular and a quadrilateral 

 portion, as in Fig. 147 or Fig. 151 ; 

 and let us now suppose the whole 

 system to grow, in a uniform 

 fashion, as a prelude to further 

 subdivision. The whole quadrant, 

 growing uniformly (or with equal 

 radial increments), will still re- 

 main a quadrant, and it is 

 obvious, therefore, that for every -^ j^j 



new increment of size, more will 

 be added to the margin of its triangular portion than to the 



