152 G. L. Kite 



solutions has been ably discussed in a recent paper by Hardy. 19 It 

 is usual to regard colloidal systems as consisting of two phases, a solid 

 and a liquid, which have been termed by Wo. Ostwald 20 the dis- 

 perse phase and the dispersion medium, respectively. 



For convenience of description arbitrary meanings will be given 

 the terms microsome and globule; the former will be restricted to 

 minute dense masses of gel, the latter to suspensions in protoplasm 

 that show many of the physical properties of oil droplets and besides 

 are usually free of protoplasm when dissected out of a cell. Most of 

 the suspensions so far found in cells fall into one or the other of 

 these groups, but intermediate forms have been observed. 



THE EGG or ASTERIAS 



The egg of Asterias is surrounded by a mass of either transparent 

 or translucent jelly which is soft and somewhat elastic and glutin- 

 ous; but it can be cut and torn to pieces and removed from the egg 

 with little difficulty. Thirty-four and six-tenths microns is the 

 average thickness of this jelly. This structure has a low viscosity 

 for a gel and is therefore extremely dilute. On many eggs, the jelly 

 has become turbid and undergone a change in refractive power and 

 as a result is visible in the usual microscopical examination. The 

 inner surface of the jelly envelope is closely applied to the outer 

 surface of the vitelline membrane which is invisible except in eggs 

 that have maturated. The vitelline membrane of the immature 

 starfish egg is a transparent and invisible solid of about two microns 

 in thickness. The physical properties of this structure are very 

 definite since it exhibits extraordinarily high viscosity, elasticity and 

 tenacity. A small piece can be drawn out into a mere thread and 

 when freed the thread contracts to a more or less rounded mass. 

 During maturation the vitelline membrane swells to two and three 

 times its original thickness, undergoes a change in refractive index, 

 and becomes quite cloudy and hence visible. In this state it is 

 softer, more glutinous and less rigid. The inner surface of this 



19 HARDY: Proceedings of the Royal Society, Series A, 1912, Ixxxvi, p. 601. 



20 OSTWALD: Zeitschrift fur chemie und Industrie der Kolloide, 1907, i, 

 p. 291. 



