Ookinesis in Ccrebratuhis Lacteiis. 387 



the new asters are formed outside the centrosomes. The centrosome 

 in section gives a granular appearance as it degenerates, and remains 

 for some time between the new aster and the nucleus. A similar 

 change takes place during the second cleavage. 



4. Rays. 

 From the metaphase to the mid-anaphase the rays are straight 

 and comparatively short; they are longer toward the vegetative pole 

 than toward the animal pole (Text Fig. C. 1). Consequently, the 

 rays cross one another much more in the vegetative region. At 

 this stage careful focussing shows that the non-fibrous rays reach the 

 j^eriphery. Through the transformation of these non-fibrous rays 

 into fibrous a beautiful display of rays ensues. Some of the rays 

 abut against the surface of the egg. Soon afterward the elongation 

 of the centrosome takes place. The rays are no longer straight; the 

 polar rays assume a fountain figure. The curvature of these rays 

 is more and more marked in later stages. ISTow the rays at the 

 "crossing" have a tendency to dissociate or draw themselves apart. 

 Text Fig. C. 4 shows the next stage where the climax of the 

 ray formation has been reached. One striking feature of this stage 

 is the formation of the sheath rays around the spindle, due to the 

 fusion of the equatorial rays and a part of the intermediate rays. 

 These spindle-shaped sheath rays seem to occur in a good many forms 

 (Wilson, 01b, p. 383, his Figs. 51-57). It should here be noted 

 that the cleavage furrow, as it deepens, cuts apart the sheath rays 

 in the middle. It is remarkable that these rays are cut without being 

 bent inwards, and still more so, since the rays thus separated begin 

 to turn away from the cleavage plane, taking a fountain figure (Text 

 Fig. C. 5). This should not be confounded, as I have already men- 

 tioned, with the antispindle figure of the anaphase. 



5. Cell Constriction and Mid-body. 

 About an hour after fertilization,-^ soon after the formation of 

 the second polocyte, a furrow appears along the animal hemisphere. 



"In the eggs taken from individuals, which had been Ivept for two or three 

 days in an aquarium, the maturation processes go on very slowly, and the 

 cleavage furrows appear an hour and a half after fertilization. 



