10 BIOLOGICAL LECTURES. 



individuals distinctly of an olivaceous or pinkish-brown color, 

 while the larger granules or microsomes are lemon yellow. 

 This circumstance makes possible an observation of great im- 

 portance, namely, that all tJie elements of the protoplasm are 

 liquid or viscid. If the eggs of Ophiura be crushed by pres- 

 sure on the cover-glass, the protoplasm flows out, most of the 

 alveolar spheres going in advance, while the granules and con- 

 tinuous substance lag behind. Meanwhile, the alveolar spheres 

 often run together to form larger drops of all sizes, the origin 

 of which is placed beyond question by their color. The same 

 is true of the yellow microsomes, though this takes place less 

 readily, and only under somewhat rough treatment. This 

 demonstrates the liquid, or at least viscid, nature of both the 

 spheres and the microsomes, and no less certainly that of the 

 continuous substance in which both lie. As far as the alveolar 

 spheres are concerned, the same observation may readily be 

 made in the colorless protoplasm of Asterias (Fig. I, c\ Echin- 

 arachnius, or Arbacia, but I could never satisfy myself of the 

 liquid nature of the microsomes in these forms. The case of 

 Ophiura renders it highly probable, however, that the granules 

 are liquid in these forms also, a conclusion which I confess 

 was a surprising result to me ; for we are so accustomed from 

 our studies on sections to regard the granules as solid bodies 

 that we are apt to forget that sections show us only coagulated 

 material. 



To sum up, a critical study of the living protoplasm of 

 echinoderm-eggs shows that it is a liquid, or rather a mixture 

 of liquids, in the form of a fine emulsion consisting of a con- 

 tinuous substance in which are suspended drops of two general 

 orders of magnitude and of different chemical nature, as indi- 

 cated by their staining reactions. The larger drops, forming 

 the alveolar spheres, stain only slightly in haematoxylin, and 

 constitute the so-called " ground-substance " in the spaces of 

 the meshwork ; these have an average size, ranging in the vari- 

 ous forms studied from i.o micron or less (Arbacia} up to 4.0 

 microns (Ophiura). The smaller drops, forming the granules 

 or microsomes, are very much more minute, and stain intensely 

 with iron-hsematoxylin. The presence of the larger drops deter- 



