LAW OF BIOGENESIS 



61 



FIG. 32. Stages in the development of three 

 crustaceans illustrating the Law of Biogenesis, or 

 the Law of Recapitulation. On the first line three 

 eggs are shown. On the second the nauplei are rep- 

 resented which hatched from the respective eggs 

 above. The middle nauplius is a good example of 

 "acceleration in development," for it is already en- 

 closed in a little shell when it hatches. The larvae of 

 its remote ancestors probably had no such shell and 

 this feature, therefore, distorts the embryological 

 record by coming earlier than in the past. The third 

 line represents the adult stages of the first two crus- 

 taceans (A 3 , J3 3 ) and what was at one time probably the adult stage in the an- 

 cestors of the third (C 3 ). The lower figure shows that the free stage shown 

 in the line above has been succeeded by a fixed, or sessile, condition. This 

 last change is accompanied by some degeneration. A, Cyclops; B, Cypris; C t 

 Balanus. 



