196 BULLETIN OF THE 



at first appear to be a fair index to the advancement of the individual 

 eggs, seems to be of secondary importance ; for in this series the one 

 (Fig. 48) presenting the least elevation is the one which, to conclude 

 from the appearance of a subsequent stage, as well as from analogy 

 with observations on the eggs of other animals, is in reality the most 

 advanced. The evidence is found in the fact that there are two zones 

 of thickenings here, while in the others only one zone is discernible. 

 It has been clearly shown, by direct observation of living cells of both 

 animals and plants, that this double zone arises by the splitting into 

 halves of the single median zone ; and that such is really the case here 

 cannot be doubted, as we shall see when we come to the investigation 

 of the next stage. Moreover, a careful examination of the figures shows 

 that the centre of the outer star is nearer the surface (whither it was 

 certainly tending) in the eggs which, for reasons just given, we must 

 conclude are the more advanced. 



The spindle, as in the preceding stage, is usually very stout, its thick- 

 ness at the equator being nearly half its length, which still remains 

 about one third the diameter of the vitellus. 



The arrangement of the granulations in the vitellus differs but little 

 from that which prevailed in the last stage. There still exists a uniform 

 distribution of these elements save where the archiamphiaster has 

 caused their more or less extensive disappearance. Corresponding to 

 the changed position of the archiamphiaster, the area of distribution is 

 somewhat modified ; but otherwise I can discover no alteration in eggs 

 subjected to hardening processes. 



The further transfer of the archiamphiaster toward the surface of the 

 vitellus is accompanied with continued changes, which affect its shape 

 more than the general form of the vitellus. Instead of pushing be- 

 fore it the thin covering formed at the animal pole, and emerging 

 from the surface as a complete spherical aster, the exposed half of the 

 outer star suffers a further and marked change of form, as well as re- 

 duction of size (Fig. 50). The centre of this stellate figure now lies 

 close to the surface of the vitellus, a thing which could only occur by a 

 displacement in the more exposed radiate fibres. What the nature 

 of that displacement is, can be inferred from what was seen in the last 

 stage, where a mechanical deflection was so apparent. 



From the position of the centre of the outer star, it follows that 

 the latter is now much less than a complete sphere ; it is even much 

 less than a hemisphere. The radial extent of the portion which re- 

 mains is, however, about the same as before, that is to say, the radiating 



