FERTILISATION OF THE OVUM 



PLATE LXXXVI 



383 



M 



N R S 



PLATE LXXXVI (continued) 



Q 



N, Separation of second polar globule (i), with two chromatin particles from the ovum ; the other two with remains of germinal 

 vesicle (d) forming the female pronucleus ; e, male pronucleus ; c, first polar globule (Carnoy). 



0. Fertilisation of the ovum of an echinoderm. u, Zona pellucida; h, spermatozoon perforating vitelline membrane; c, proto- 

 plasm of vitellus. 



P. a, Zona pellucida ; ft, entrance of spermatozoon into protoplasm of vitellus (c), with radiating and concentric arrangement 

 of its granules. 



Q. a, Zona pellucida ; 6, head of spermatozoon enlarging to form male pronucleus ; d, female pronucleus. The radiating and 

 concentric arrangement of protoplasmic yolk granules is well marked in this figure. 



R, S. Blending of the male (b, b) and female (d, d) pronuclei (Selenka). 



PLATE LXXXVII 



Plate Ixxxvii. illustrates different stages of karyokinesis in the epithelium cells of the larva of the salamander. 

 These cells are hardened in chromic acid and stained with hajmatoxyhn. Highly magnified (Flemming). 



A. Resting cell, displaying the nuclear network. 



B. First stage of division, the chromoplasm being converted into a skein of closely contorted filaments. 



0. Second stage of division, filaments increased in size and less closely arranged. (In this and all the other figures, Fig. A 

 excepted, the nuclear matrix is clear.) 



D. Filaments slightly more magnified than in the other figures ; these showing a looped arrangement, better seen at E, where 

 they are rosette-shaped and enclose a central clear space. 



F. Filaments converging towards the centre. 



G. Stellate phase or aster. 



H. Completion of longitudinal splitting already begun at P and G. 



1. Filaments beginning to separate into two groups (metakinesis). 

 J. Further separation into two sets. 



K. Separation further advanced. 



L. Stellate phase of daughter nuclei (diaster). 



M. Commencing convolution of filaments. 



N. Filaments more contorted. 



0, P. Gradual passage of daughter nuclei into condition of rest as seen at network Q. 



Note.— The division of the protoplasm begins at the stage (M) and is rapidly completed at (N). 



