Fig. loi. Physiological gradients in the egg of the lamprey (Hyman). 23-26. Early 

 blastula, 24 hours. 27-31. Late blastula, 40 hours. 32-35. Beginning of gastrula- 

 tion, 48 hours. 36-39. Gastrula, 60 hours. 40-43. Late gastrula, 70 hours. 44-46. 

 Late gastrula, neural groove about to appear, 75 hours. From no. 36 onwards, the 

 anterior end is to the right. 



