8o ANDREWS. 



ual cell-masses; the other to position, with relation to the whole 

 mass of the embryo. 



According to the point of time in each of these sets of 

 varying rhythms, did the viscosity, elasticity, and resistance to 

 pressure, of the mass or area vary ; also the specific reaction 

 of the substance when brought artificially in contact with 

 water. 



From the first it is true, that those portions which lie inter- 

 nally to the embryo as a mass are more fluid; and conversely, 

 that the more peripheral portions are more viscous and resistant. 



Internally to each cell also, whenever it stands separate, 

 except for the filaments, from the mass, or its sister cell ; there 

 is always an area of more fluid substance. 



After each cell again becomes firmly welded to the mass, or 

 to its sister cell, that portion which is internal to the whole 

 mass as then formed, becomes more fluid, without respect to the 

 number of cells. 



This seeming sensitiveness of the substance to its position 

 in the common mass is the more remarkable since tJie centre of 

 the group is a cavity full of the same watery efivirojiment as sur- 

 rounds the periphery, because the conditions then would seem 

 to be identical for all the peripheral substance, yet it reacts 

 differently at different points with little or no regard to this. 



In the four-celled stage, when the cells are sometimes firmly 

 welded together for long minutes, there was marked fluidity of 

 those portions, including the pellicular wall, which projected 

 inwards towards the cleavage cavity. From this portion the 

 filose processes extended, filling the cavity with a protoplasmic 

 web. Yet the firmly knit and relatively very viscous peripheral 

 portions were no less active in this respect. When a more fluid 

 area comes in the rhythm to lie between two sister cells, the 

 cell walls also share in the relaxed physical state. 



[89] The viscosity of the substance is, then, rhythmically 

 modified according to its temporary position with respect to 

 external environment of the whole embryo ; greater or less 

 fluidity being assumed in the same region of a cell or the mass, 

 according to its position as internal or external to that organ- 

 ization of the living substance. (See Substance as Organism — 



