478 WILSON. 



EXPLANATIONS OF PHOTOTYPES 9-12. 



Phototype 9. The egg immediately before division (50 minutes), showing 

 the chromosomal vesicles, the vagueness of the centrosphere and the beginning of 

 the mid-body (cf. Text-fig. VIII, B, p. 461). 



Phototype 10. The beginning of cleavage (50 minutes). Daughter-nuclei 

 re-forming. The mid-body distinct (Text-fig. IX, p. 462). 



Phototype ii. Cleavage nearly completed. The daughter-nuclei are re- 

 formed, spindle and mid-body have disappeared, and the asters have assumed a 

 horse-shoe shape preparatory to division (cf. Text-fig. X, A, p. 464). 



Phototype i 2. Two-cell stage after division of the asters, in the pause (60 

 minutes). Growth of the daughter-nuclei. No centrioles can now be seen in the 

 asters (cf. Text-fig. X, B, p. 464). 



