MATURATION AND IMPREGNATION OF THE OVUM. 54! 



tion the protoplasm in its neighbourhood assumes a radiate 

 arrangement (Fig. 15). At whatever point of the egg the 



FIG. 15. Ovum of Asterias glacialis, with male and female pronucleus and a radial 

 striation of the protoplasm around the former. From living ovum (copied from 

 Fol). 



spermatozoon may have entered, it gradually travels towards the 

 female pronucleus. This latter, around which the protoplasm 

 no longer has a radial arrangement, remains motionless till it 

 comes in contact with the rays of the male pronucleus, after 

 which its condition of repose is exchanged for one of activity, 

 and it rapidly approaches the male pronucleus, and eventually 

 fuses with it (Fig. 16). 



FIG. 16. Three successive stages in the coalescence of the male and female pronu- 

 cleus in Asterias glacialis. From the living ovum (copied from Fol). 



The product of this fusion forms the first segmentation nucleus 

 (Fig. 17), which soon, however, divides into the two nuclei of the 

 two first segmentation spheres. While the two pronuclei are 

 approaching one another the protoplasm of the egg exhibits 

 amoeboid movements. 



Of the earlier observations on this subject there need perhaps 

 only be cited one of E. van Beneden, on the rabbit's ovum, 



