THE LIVING SUBSTANCE. iqi 



series of changes and much wandering, they become more 

 and more restricted in each half the mass to their own side 

 of the plane of the coming cleavage. About this time, begins 

 an irregular fusing of the tips of aster rays with each other, 

 along the course of the coming plane. At first they form by 

 this means a crooked sort of network rather parallel to the 

 cleavage plane. This becomes more and more straightened 

 out in its own plane, and at the same time there is a slight, 

 but perceptible, increase of interalveolar stuff along the same 

 plane between the alveoli, or, perhaps, merely a spreading 

 out there of the substance of the fusing rays. At last there 

 is a distinct pellicular, or plate-like, thickening along the 

 coming cleavage plane. ^ 



The same process being gone through with on both sides 

 the same line, the pellicular plate is double in origin, although 

 optically single. On each side of it for a variable time is a 

 perfect alveolar layer of vesicles which are unlike the others 

 of that central region of the cytoplasm, being small and like 

 those of the general periphery ; with this they are, in short, 

 continuous in all optical appearance, being truly a preformed 

 continuation of it. At this time the rays which spring from 

 the " attraction sphere " are very long and in general fused at 

 their tips with the general peripheral pellicle. At the same 

 time similar thickenings of interalveolar substance are seen, 

 tapering from their point of origin as they pass inwards, and 

 ending in undifferentiated continuous substance before they 

 reach the centrosome. This they never very closely approach 

 since the true astral rays maintain precedence upon the alveolar 

 structure. 



Although during actual cleavage the astral rays, or certain 

 of them, show transiently rhythmic changes which charac- 

 terise true contractile fibres, I do not think that the cleavage 

 may be assigned to this alone. For, there is a wave-like 

 shrinking apart of the double pellicular plate, which is inde- 

 pendent of the rays and which doubtless assists, and could 

 accomplish it alone. It is of the same nature as the activity 



^ A somewhat similar plate-like formation was described by Camoy for Nema- 

 tode eggs, but of this I knew nothing at time of my observations. 



