492 ROBEKT CHAMBERS, JR. 



eggs for the production of artificial 'astrospheres' (Morgan, '96, 

 '99) and cytasters (Wilson, '01 a and others including Yatsu, '05) 

 possibly cause a localization of the sphere liquid in several 

 centers instead of allowing a flow into a single sphere. 



2. The formation of the aster 



The development of the aster was studied from the moment of 

 its appearance on the entrance of the sperm into the egg, until 

 the egg had segmented into eight cells and numerous dissections 

 were made in the various stages. Because of the beautiful 

 transparency of the Echinarachnius egg the different stages of 

 the aster were best followed in this form and the following 

 remarks, unless otherwise stated, apply to it. 



Within two or three minutes after the entrance of the sperm and 

 in the vicinity where it entered, a tiny aster appears which rapidly 

 grows in size and extent. From the beginning it contains a 

 liquid center of appreciable size. That the cytoplasm about this 

 center has been rendered fairly solid is shown by the fact that the 

 aster at this stage may be pushed and rolled in the surrounding 

 liquid cytoplasm (fig. 5). The sperm nucleus is held in the gel 

 around the sphere (fig. 6), -and is therefore dragged about with 

 the aster. The aster grows while at the same time the sphere 

 increases in size evidently by a centripetal flow of liquid in the 

 rays. The cytoplasm lying between the rays increases in rigiditv 

 as the gel state gradually extends in area. 



During this time the eccentrically placed aster moves to the 

 egg center. The shifting in position is possibly due to unequal 

 pressure exerted at its periphery as the aster extends in area. 

 An equilibrium obtains when the aster finally comes to rest at the 

 center of the egg. As the sphere increases in size the sperm 

 nucleus comes to lie in it. The nucleus may be dragged out of 

 the sphere but as long as it is within the confines of the aster, it 

 will, on being released, move slowly back into the sphere. As 

 the aster slowly moves towards the center of the egg, its growth 

 extension is heralded by a streaked appearance of the surrounding 

 cytoplasm. The streaks run in the direction of the converging 

 rays and are due to a gradual gelation of the granular 



