ARTIFICIAL PARTHENOGENESIS OF ASTERIAS. 163 



ferent categories with respect to their effect on the egg, but they 

 both produce similar results in a continuous process of activation, 

 the second carrying forward the activation effects caused by the 

 first, whatever that may have been." 



DISCUSSION. 



Cytological studies on the maturation phenomena of artificially 

 activated eggs of Astcrias, show this process is subject to wide 

 variations in the history of both the chromatic and achromatic 

 figures. It has been shown that maturation may take place with 

 one, two, or no polar bodies extruded. The eccentric monaster is 

 the primary phase of both achromatic figures, which in eggs 

 properly activated may by division give rise to normal amphiaster 

 and lead to the extrusion of each polar body. This process is 

 also subject to wide variation both in number and arrangement 

 of nuclear asters and their secondary union with cy tasters. 



The evidence in this paper shows the normal type of matura- 

 tion following artificial activation involves the extrusion of two 

 polar bodies. The dissolution of the nuclear membrane is fol- 

 lowed by the appearance of a minute aster in the cytoplasm just 

 outside the remnant of the germinal vesicle at a point nearest the 

 surface of the egg. The aster divides to form the amphiaster 

 which extrudes the first polar body. The inner aster with its 

 central body soon degenerates and is soon lost to view. The sec- 

 ond polar spindle is formed by the division of a monaster that 

 arises " de novo " on the median side of the scattered chromo- 

 somes. The second polar spindle extrudes the polar body and 

 degenerates as did the first polar spindle. Tennent and Hogue 

 ('06) maintain that this is the only type of maturation that will 

 give rise to normal larv?e. 



The second most common type of maturation in artificially 

 activated eggs of Astcrias forbcsii involves the extrusion of only 

 one polar body. The polar spindles are formed as in normal 

 maturation, but the second polar spindle fails to migrate to the 

 surface of the egg and extrude the polar body. Division takes 

 place submerged and forms two nuclei with apparently normal 

 chromatin content. The usual subsequent action of these two 

 nuclei is to fuse and form the cleavage nucleus with the diploid 



