286 LILLIE. 



become much smaller. The sperm-nucleus is contracting, and may be seen to be 

 composed of about sixteen chromatic vesicles. Only those of one surface shown. 



Fig. 9i5. Sperm-nucleus of another egg in the same stage of maturation, to 

 show the vesicular structure. 



Fig. io. Tangential section through the outer aster in the stage of Fig. 9, to 

 show the concentric spheres, inner and outer, and the rays penetrating to the 

 dumb-bell-shaped centrosome. 



Fig. II. First maturation spindle just before the beginning of the protrusion 

 of the first polar globule. The centrosomes at each end are double, and the chro- 

 mosomes are assuming the form characteristic of the second maturation division, 

 thus repeating their form in the first maturation spindle. The microsomes are 

 beginning to grow large in the interzonal region where the stress has ceased. 

 Cf. Fig. S. 



Fig. 12. First maturation spindle. In this stage the two centrosomes of each 

 inner sphere are distinctly compound, double or quadruple. The enormous size 

 of the microsomes in this stage is especially noticeable. The chromosomes have 

 completely assumed the form characteristic of the second maturation division. 



Fig. 13. Constriction of first polar globule. The inner sphere and group 

 of chromosomes have moved bodily near to the surface, to which they are 

 attached by a new set of radiations. The sphere remaining in the egg is smaller 

 than in the preceding stage (Fig. 12), and the centrosomes within it are closer 

 together. 



Fig. 14. The first polar globule is fully formed, but is still attached by means 

 of " Zwischenkorper " fibers to the surface of the egg. (These were found in the 

 next section, which is not figured.) The centrosomes of the egg-sphere are now 

 in contact, and the radiations which in Fig. 9 extend from the sphere to the surface 

 have now been resolved into vesicular cytoplasm. 



