350 KING. 



EXPLANATION OF PLATE XXXI. 



Fig. 48. The male pronucleus about fifteen minutes after the egg has been 

 fertilized. The radiation around the pronucleus centers in the astrosphere which 

 is in the next section of the egg. Zeiss apoc. 2 mm., Oc. 8. 



Fig. 49. The female pronucleus beginning its migration from the surface. 

 About fifteen minutes after fertilization. Zeiss apoc. 2 mm., Oc. 8. 



Fig. 50. The two pronuclei approaching each other about one-half hour 

 after fertilization. The male pronucleus lies between the two centers into which 

 the astrosphere has divided. Zeiss apoc. 2 mm., Oc. 8. 



Fig. 51. Apposition of the two pronuclei about three-quarters of an hour 

 after fertilization. Zeiss apoc. 2 mm., Oc. 8. 



Fig. 52. A somewhat oblique section showing the resting daughter nucleus 

 with its astrosphere preparing to divide into two parts in preparation for the sec- 

 ond cleavage. Zeiss apoc. 2 mm., Oc. 8. 



Fig. 53. Formation of the segmentation spindle by the union of rays from the 

 two astrospheres. The segmentation nucleus has rounded up and occupies a posi- 

 tion at the equator of the forming spindle. Zeiss apoc. 2 mm., Oc. 8. 



Fig. 54. The segmentation spindle after the breaking down of the segmenta- 

 tion nucleus. The chromosomes lie at the equatorial plate of the spindle ; the 

 astrospheres have reached their greatest extent. (A combination of two sections.) 

 Zeiss apoc. 2 mm., Oc. 8. 



Fig. 55. Metaphase of the segmentation spindle. Decrease in size of the 

 astrospheres and disappearance of many of the rays. (A combination of two 

 sections.) Zeiss apoc. 2 mm., Oc. 8. 



Fig. 56. The segmentation nucleus. The section is cut somewhat obliquely, 

 so that only one astrosphere is shown. Zeiss apoc. 2 mm., Oc. 8. 



