THE CELL ASTER 503 



Wilson, E. B., and Mathews, A. P. 1895 Maturation, fertilization, and polar- 

 ity in the echinoderm eggs. Jour. Morph., vol. 10 pp. 319. 



Yatsu, N. 1905 The formation of centrosomes in enucleated egg-fragments. 

 Jour. Exp. ZooL, vol. 2, p. 287. 



ZsiGMONDY, R. 1905 Zur Erkenntnis der Kolloide. Jena: G. Fischer. Trans, 

 by J. Alexander. New York: Wiley. 



PLATE I 



EXPLANATION OF FIGURES 



The figures are all sketches from living eggs. Figures 1 to 13 are of the Echin- 

 arachnius egg, figures 14 to 20 of Cerebratulus. Figures 1, 2, 10, 14, 15 and 17 

 to 20 purport to be more or less faithful representations. The remainder are 

 diagrams in which the astral radiations are merely indicated by lines. 



The tip of the needle when shown is represented by a small circle with a central 

 spot. 



1 Enlarged drawing of the tapering tips of the gelled cytoplasm (with em- 

 bedded micro- and macrosomes) projecting between bases of the hyaline liquid 

 rays into the periphery of the sphere. 



2 The same as figure 1 but with the tips bent to one side by the microdis- 

 section needle. 



3 Diagram to show the distortion of astral radiations by inserting the needle 

 into the aster and moving the needle in a straight line. 



4 Nucleus in a fully formed aster pushed to one side with a needle thus causing; 

 distortion and stretching of the astral radiations. 



5 Early sperm aster spirally twisted in shape by moving it through the 

 liquid cytoplasm with a needle. 



6 Inserting the needle into the sperm nucleus and pulling draws the nucleus 

 out into a ribbon-shaped mass showing that the nucleus is held in a gelatinous 

 mass. On being released the nucleus reverts to its original spherical shape. 



7 Fusion nucleus lying to one side in the sphere so that the sphere-liquid 

 extends like a cap around one side of the nucleus. 



8 Nuclear 'spindle' becoming bipramidal in shape as the sphere-liquid begins 

 to collect at its two poles. Rays beginning to disappear around the equator. 



9 Hyaline plasma collected at the nuclear poles to form two spheres. Begin- 

 ning of the amphiaster. 



10 Amphiaster in living egg of the Echinarachnius. The drawing shows 

 only the central portion of the amphiaster. The clear area extending between 

 the two asters represents the hyaline nuclear 'spindle.' The chromosomes 

 have been omitted in the drawing. Scattered microsomes mark off the ends of 

 the 'spindle' from the sphere. 



11 Nuclear 'spindle' beginning to take on the form of a dumb-bell. The 

 cytoplasmic granules in the equatorial region about the nuclear constriction 

 become visibly mobile at this stage indicating an increase in the fluidity of that 

 region. 



12 The needle inserted into the nuclear 'spindle' has pulled it to one side in 

 the cell dragging the astral radiations along with it. 



