192 BULLETIN OF THE 



evenly distributed through its mass, save where they come within the 

 reach of the influence which determines the differentiation of the sub- 

 stance of the maturation figure into less refractive and more refrac- 

 tive fibrous portions having a definite arrangement. Here these coarse 

 deutoplasmic elements are made to assume a corresponding radial rela- 

 tion. They decrease in abundance toward the centres of the stellate 

 figures. 



The figure of the whole vitellus is that of a sphere, which may already 

 be slightly flattened in the direction of the only diff'erentiated axis.* 

 The portions which are most deeply stained in carmine are, first, the 

 equatorial thickenings of the spindle, and after them the central 

 portions of the two asters. The gradual increase from periphery to 

 centre in the density of each aster makes it more and more difficult, as 

 one approaches the centre of the star, to distinguish the compact proto- 

 plasmic rays from the protoplasm in which they are imbedded. For 

 this reason the '' area " is not always at this time a region definitely 

 circumscribed by the central terminations of the radial fibres. 



In the stage just reviewed we have seen the first archiamphiaster 

 fully formed, and already advanced to a position such that a continua- 

 tion in its motion of translation will necessarily make itself at once 

 apparent in the general outline of the yolk. Such a modification is, in 

 fact, the thing which, in the next stage (Figs. 43, 48), most forcibly 

 attracts attention, — not, however, in the manner one might have antici- 

 pated. The whole vitellus becomes conspicuously flattened in the direc- 

 tion of its polar diameter, and at the same time presents at the animal 

 pole, as a sort of compensating change, a slight elevation. The latter 

 becomes prominent in proportion as the vitellus, as a whole, undergoes 

 further depression at this pole of the egg. It is as though the vitellus 

 at the animal pole were to sink gradually away, leaving the peripheral 

 end of the archiamphiaster protruding beyond the general outline. The 

 latter, as seen from either pole of the main axis, remains that of a circle, 

 or at least presents only very slight and inconstant deviations from that 

 form ; but the outline, as seen in profile, becomes altered, not simply, 

 as it would seem, by the protrusion of the maturation figure, but by a 

 concomitant flattening of the adjacent portions of the vitellus. The 

 relation of these two acts to each other and to their cause will be con- 

 sidered hereafter. The resulting outline is like that produced by the 

 insertion of the arc of a smaller circle into that of a greater one. The 



* For the peculiar appearance of the outline at the animal pole of the vitellus in 

 Fig. 45, see the explanation of the figures. 



I 



