PROTOPLASM OF ECHINODERM EGGS. 143 



I do not mean to imply that these granules are hard insoluble 

 granules because many of them, as Wilson has pointed out, ap- 

 pear more fluid than solid, but I mean that the actual structure 

 of protoplasm is more clearly and accurately represented as a 

 clear homogeneous viscid matrix, in which oil globules and all 

 sorts and sizes of granules are embedded than as an alveolar 

 structure. 1 An alveolus is a hole in a matrix. It is not the hole, 

 but the matrix, which in my opinion is the important part of 

 protoplasm. 



If one seeks for a substance most nearly resembling proto- 

 plasm in structure, raspberry jam, were it colorless, would fairly 

 accurately represent what one sees a clear sticky matrix in 

 which are a multitude of seeds. 



In none of the eggs while living could I see any trace of spin- 

 dle fibers or of fibers at all like those seen in sections. When the 

 egg is fixed, the proteid colloids which in solution constitute the 

 larger part of the clear viscid matrix, are precipitated in a granu- 

 lar form. In other words, the clear matrix appears to represent 

 a colloidal solution in which our fixing agents throw down a pre- 

 cipitate. The appearance of rays seen in fixed preparations is 

 quite different from appearances in the living egg. In the living 

 egg the clear protoplasm sends off radiating broad strands toward 

 the periphery of the cell. In fixed preparations the rays appear 

 a great deal stiffer and much finer, not so broad as the clear bands 

 although they occupy the position of the living radiations. 



These observations indicate very clearly to my mind that the 

 protoplasm of these eggs is essentially a viscid colloidal solution 

 something like gum arabic in viscidity and embedded in it are 

 precipitated or undissolved granules. It may be regarded as 

 a partially precipitated, colloidal solution and the ease with which 

 the granules may be made to dissolve in the clear matrix, indi- 

 cates, I think, that the amount of precipitate and number of these 

 granules must be constantly changing. Protoplasm appears to 

 be in fact a two-phase colloidal system, undergoing spontaneous 

 chemical change, and surrounded by a semi-permeable membrane. 



The changes the granules undergo in the living egg when the 

 latter is compressed or burst are extremely difficult to follow and 



1 From Asferias eggs large quantities of an oil may be separated. 



