THE VITAL PHENOMENA OF THE CELL 219 



plane of the contingent surfaces, that is to say, in the so-called 

 conjugation plane. If this were to occur here, the spindle axis, 

 contrary to the above-mentioned law, would cut the longitudinal 

 axis at right angles, the centrosomes would be placed in the 

 neighbourhood of the least amount of protoplasm, and finally, the 

 first division plane would have to divide the egg longitudinally. 



A proceeding so contrary to law does not occur here, for the 

 protoplasm and nucleus, whilst reacting on each other, subse- 

 quently regulate their finally assumed positions, which are in 

 accordance with the conditions present. The original position of 

 the conjugating pair of nuclei, which is brought about by the pro- 

 cess of fertilisation, and which is quite unsuitable for the pui-poses 

 of division, becomes changed, whilst the two poles become more 

 clearly defined. The nuclear pair commence to turn themselves 

 through a right angle (Fig. 110 B), until the conjugation plane co- 

 incides with the longitudinal axis of the egg (Fig. 110 C). 



" Sometimes they rotate in the same direction as the hands of a 

 watch, sometimes in the opposite direction" (Auerbach). 



In consequence of this interesting phenomenon of rotation, the 

 two poles of the division figure come to be in the neighbourhood 

 of the largest accumulation of protoplasm, in accordance with the 

 law, whilst the smallest amount is situated near the division plane, 

 which develops later (Fig. 110 D). 



A second instance of the truth of this law is afforded by the 

 experiments of Pfliiger (VI. 49, 50) upon Frogs' eggs. He care- 

 fully compressed a freshly-fertilised egg between two vertical 

 parallel glass plates, thus giving to it pretty nearly the form of 

 " a much-flattened ellipsoid, of which the longest axis is horizontal, 

 the one of medium length vertical, and the shortest again horizon- 

 tal and perpendicular to the longest." In nearly every case the 

 first division plane was vertical to the surface of the compressed 

 plate, and at the same time perpendicular. Hence the nuclear 

 spindle must again in this case, in accordance with the above- 

 mentioned law, have placed itself in the direction of the longest 

 diameter of the ellipsoid. 



From this law, that the position of the nuclear axis in division 

 is determined by the differentiation and form of the surrounding 

 protoplasmic body, so that the poles place themselves in the 

 direction of the greatest collection of protoplasm, we can deduce 

 a third law, which Sachs (VI. 64) arrived at from a study of plant 

 anatomy, and has described as the law of rectangular intersection 



