THE STRUCTURE OF PROTOPLASM. 5 



merable minute granules, or microsomes, suspended in a clearer, 

 less deeply staining, continuous substance (Figs. I, a, and 4). 

 The spaces of the meshwork, which measure from one to nearly 

 two microns, are occupied by a third substance, clear, homo- 

 geneous, and of only slight staining capacity, which has often 

 been called the ground-substance. During cell-division, the 

 meshwork in the neighborhood of the dividing nucleus assumes 

 a radiating appearance, giving rise to the so-called asters, or 

 astral systems which are typically double, forming the amphi- 



FIG. i. (a) Protoplasm of the egg of the sea-urchin (Toxopneustes) in section ; (b) protoplasm 

 from a living star-fish egg (Asterias); (c) the same in a dying condition after crushing 

 the egg; (d) protoplasm from a young ovarian egg of the same. (All the figures mag- 

 nified 1200 diameters.) 



aster (Fig. 3, b). We may define the problems suggested by 

 these appearances by a series of questions as follows : 



1 . What is the actual structure that gives the appearance of 

 a meshwork ? 



2. How faithfully does the preserved structure, as seen in 

 sections, reproduce that existing in life ? 



3. What is the relation of the astral systems to it? 



4. What is the finer structure and origin of the meshwork ? 



5. Can this structure be taken as typical of all protoplasm; 

 and if not, what is its relation to other forms of protoplasmic 

 structure ? 



After seeking for answers to these queries, we may finally 

 inquire how they bear on the theoretical views briefly reviewed 



