THE LIVING SUBSTANCE. 57 



Substance differentiation as seen in Protoplasts was illus- 

 trated above by a specific description, for v^hioh Amcsba protetis 

 was used. For differentiation of the living structure as found 

 in Metazoan organisms, a starfish tgg watched through its 

 development is, perhaps, as beautiful a typical illustration as 

 the student can have. As it lies in the water before matura- 

 tion with its nuclear sac still perfect, it presents to the eye a 

 mass of living substance having already area within area of 

 pellicular and alveolar organization. Thereafter the history of 

 development is truly a record, from moment to moment, of 

 more or less unstable permutations, transmutations, and meta- 

 morphoses of such structural differences, having complex, 

 rhythmical relations to the substance as such, to the substance 

 as organism, and to the life history of the race substance. 



At such a time as I have chosen, there is seen within the 

 outer protoplasmic pellicle of the egg the mass of general cyto- 

 plasmic substance, where changeful rearrangements of the 

 foam vesicles arise and pass like dissolving views. The 

 vesicles of Butschli's structure have seldom a spherical, but 

 rather an irregular contour. They are drawn out of shape still 

 more from moment to moment by local tensions in the inter- 

 alveolar foam. 



Within the general cytoplasmic area comes the nuclear area 

 surrounded by its own pellicle which, in those cases examined, 

 was formed of very small vesicles bounded on either side by 

 pellicles of continuous substance. It was most like those 

 intra-cellular formations which later form the new cell walls. 

 The surface of this nuclear membrane yielded at times under 

 favorable optical conditions finer vesicular contours which 

 produced the " shagreen " effect. 



At this stage, the general nuclear area is a much less dense, 

 and optically much more fluid-seeming, area than the cytoplasm. 

 That it is actually so was proven by pressing the nuclear con- 

 tents out into the water through a mechanical rupture of this 

 membrane and the Q.gg membrane. Yet this nuclear area 

 contains local modifications of its vesiculation, which have pro- 

 nounced viscosity over that of the cytoplasmic area even. 

 These are variably numerous, smaller, spherical areas, which 



