THE LIVING SUBSTANCE. 85 



themselves up on all sides, except those of the cleavage plane 

 which were connected by filaments. Finally, after a number 

 of changes of form, these sides, which were then rather flat- 

 tened, approached each other more and more, while the 

 protoplasmic bridges showed greater homogeneity and even 

 structurelessness, with increase of viscosity and refractiveness. 

 They thickened too, in many instances, as the cell surfaces 

 drew together, until at last the pellicular surfaces were too close 

 to admit of further observation. 



In sea-urchin eggs, the spinning phenomena were fundamen- 

 tally the same ; the filose processes, however, were less profuse 

 and finer. Similar varying rhythms of viscosity, and flux of pel- 

 licular and interalveolar substance were also observed. In this 

 form the segregation at certain rhythmic intervals, or rather in 

 certain rhythmic progressions, of pigment granules from certain 

 portions of the cytoplasm was interesting and suggestive, not 

 only in connection with a flux of continuous substance along 

 lines of the meshwork and pellicles, but as correlated with 

 structural preparation of certain areas for specific physiological 

 function. Before each early cleavage, pigment granules were 

 carried along the pellicles in a flux of substance towards the 

 line where the split was to take place, and appeared to be 

 carried onwards and inwards from this point, but about this last 

 there is yet some doubt in my mind. 



In rotifers' eggs a similar segregation of yolk is extremely 

 marked, the very planes of cleavage being thus for a long time 

 clearly indicated before there is any other sign of an order of 

 cleavage among the cells. 



Such phenomena are thoroughly in accord with the general 

 habit of the substance in withdrawing interalveolar substance 

 to an area where its activities when organized will not be ham- 

 pered by inelastic, or irregular, inclusions ; or of withdrawing 

 the inclusions to another place. The areas cleared of yolk in 

 segmenting eggs are noticeably areas in which are about to 

 take place organized contractile activities, as amphiastral areas, 

 or cleavage planes. 



Pigment, yolk, and granules are carried thus in instances 

 from cell to cell. Flux of interalveolar and pellicular substance 



