FIG. 52. Figures illustrating four different kinds of cleavage. A, equal 

 cleavage of the sea urchin egg; B, unequal cleavage of the egg of 

 marine worm ; C, discoidal cleavage of the egg of a squid ; D, superficial 

 cleavage of an insect's egg. (A-B, from Wilson ; C, from Wilson aftei 

 Watase; D, from Korschelt and Heider.) 



