EXPLANATION OF PLATE III. 



Stages in the fertilisation of the egg of the Axolotl, after JENKINSON. 



a. The sperm head (becoming vacuolated) and part of the tail. The middle- 

 piece has disappeared and is represented by vacuolated protoplasm with 

 radiating alveoli, on the walls of which are pigment granules. 



b. The sperm head has swollen to form a nucleus. A centrosome has appeared 

 in the centre of the alveolar radiations, and is dividing. 



c. The daughter-centrosomes have separated to opposite sides of the con- 

 jugating egg and sperm nuclei. 



d. First segmentation division. Equatorial plate stage represented on the left, 

 early anaphase on the right. On the left, a centrosphere has been formed 

 by reticular degeneration of the inner rays, and within it a vacuolated cen- 

 trosome. Spindle of irregular fibres with pigment on the outer rays. On 

 the right, a homogeneous centrosome has appeared, containing a centriole 

 which divides in the late anaphase in preparation for the succeeding nuclear 

 division. (Redrawn from Quart. Journ. Micr. Sci. XLVIII. Pis. 30, 32, 33.) 



