336 WILSON AND MATHEWS. [Vol. X. 



somes of the &%^ are derived at maturation either from the 

 interior of the germinal vesicle or from its wall, and escape 

 from it on the rupture of the latter. 



B. Fertilization of Asterias forbesil 



The sperm enters either ripe or unripe eggs at any point of 

 the periphery, and in ripe eggs an attraction-cone such as is 

 figured by Fol is formed. In unripe eggs many sperms enter, 

 no vitelline membrane appears, the archoplasm remains insig- 

 nificant, and either precedes or follows the sperm-head until 

 the latter finally arrives at the germinal vesicle-wall, where it 

 comes to rest. In ripe eggs dispermy is common, but not 

 normal. The sperm enters these eggs before or during matu- 

 ration, but the sperm-aster remains insignificant until the dis- 

 appearance of the wall of the germinal vesicle (see Fig. 5, 6"). 

 Owing to the difficulty of orienting the sperm-head after pene- 

 tration, it has been found impossible to say, with certainty, 

 whether the sperm-aster develops from the tip or base of the 

 sperm, or whether the latter rotates or not (see Fig. 5, F). 

 Before penetration the deeply staining sperm-nucleus is seen 

 to have in front of it a red-staining tip, and behind it a red-stain- 

 ing middle-piece (see Fig. 5, E). In ripe eggs the undivided 

 sperm-star precedes the sperm-head as it penetrates. 



While the polar bodies are forming, the sperm star is devel- 

 oping and, at about the time of formation of the second polar 

 spindle, or later, divides (see Fig. 6, A). After division the 

 stars grow rapidly, the archoplasm-mass becomes very large, 

 and in favorable sections is seen to consist of a reticulum, the 

 nodes of which in less favorable preparations appear to be co- 

 agulated into one, two, three, or more granules like centro- 

 somes (see Fig. 6, B). From the periphery of these spheres 

 conspicuous rays develop, penetrating the eg^ in all direc- 

 tions. There is thus formed a large sperm-amphiaster of 

 which one aster precedes and the other follows the sperm- 

 nucleus during its further course. This is in striking contrast 

 to the process in Arbacia and Toxopneustes. Meanwhile the 

 sperm-nucleus has become vesicular, and at the time of conju- 



