IV] STRUCTURE OF THE CELL 193 



matter by saying that, if you have caryokinetic figures developing 

 inside the cell, that of itself indicates that the dynamic system 

 and the locahsed forces arising from it are in continual alteration ; 

 and, consequently, changes in the outward configuration of the 

 system are bound to take place. 



As regards the phenomena of fertihsation, — of the union of 

 the spermatozoon with the "pronucleus" of the egg, — we might 

 study these also in illustration, up to a certain point, of the 

 polarised forces which are manifestly at work. But we shall 

 merely take, as a single illustration, the paths of the male and 

 female pronuclei, as they travel to their ultimate meeting place. 



The spermatozoon, when within a very short distance of the 

 egg-cell, is attracted by it. Of the nature of this attractive force 

 we have no certain knowledge, though we would seem to have 

 a pregnant hint in Loeb's discovery that, in the neighbourhood 

 of other substances, such even as a fragment, or bead, of glass, 

 the spermatozoon undergoes a similar attraction. But, whatever 

 the force may be, it is one acting normally to the surface of the 

 ovum, and accordingly, after entry, the sperm-nucleus points 

 straight towards the centre of the egg ; from the fact that other 

 spermatozoa, subsequent to the first, fail to effect an entry, we 

 may safely conclude that an immediate consequence of the entry 

 of the spermatozoon is an increase in the surface-tension of the 

 egg*. Somewhere or other, near or far away, within the egg, hes 

 its own nuclear body, the so-called female pronucleus, and we 

 find after a while that this has fused with the head of the sperma- 

 tozoon (or male pronucleus), and that the body resulting from 

 their fusion has come to occupy the centre of the egg. This must 

 be due (as Whitman pointed out long ago) to a force of attraction 

 acting between the two bodies, and another force acting upon 

 one or other or both in the direction of the centre of the cell. 

 Did we know the magnitude of these several forces, it would be 

 a very easy task to calculate the precise path which the two 

 pronuclei would follow, leading to conjugation and the central 



* But under artificial conditions, "polyspermy" may take place, e.g. under 

 the action of dilute poisons, or of an abnormally high temperature, these being 

 all, doubtless, conditions under which the surface-tension is diminished. 



T. G. 13 



