,.-Of|j^ 



■■^afet- 



Fig. lOO. Physiological gradients in the egg of the lamprey (Hyman) . 1-4. Unfertilised 

 egg. 5-8. Four-cell stage. 9-12. Eight-cell stage. 13-18. About thirty-two-cell 

 stage, 16 hours. 19-22. Morula, 20 hours. 



