Dynamic Theory. 



FIGS. 49, 50, 51, 52. 



FIG. 49- Eg? of cod. a. Germ with nucleus. 6. Egg membrane, c. Ball ofnutri- 

 tive yelk, d Globule of fatty matter. 



FIG- 50. Beginning of segmentation of germ disc (2 cells). Letters same. 

 FIG. 51. Mulberry germ of disc gastrula. Letters same. 

 FIG. 52. Little fish formed from the disc within the shell. 



FIG. 53. FIG. 54. 



FIG. 53. Young salmon just out of the egg, surrounding its yelk sac 

 FIG. 64. -Young salmon three or four days out of the egg swimming with yelk sac at- 

 tached. 



FIG. 55 Little white fish escaped 

 trom the egg and swimming about with 

 the nearly exhausted yelk sac c still at- 

 tached to him. This he does about 60 

 days after the egg is laid, but his devel- 

 opment is still very incomplete mouth 

 is underneath, teeth not formed, fins 

 have no rays, and the gill covers not yet 

 formed. Yelk sac diminishes daily and 

 FIG. 55. soon disappears. 



pie existence as a cell by metamorphosis and modification of the cell 

 into other forms, and their continued growth to maturity consists sim- 

 ply of a series of continued metamorphoses and modifications, each one 

 of which depends upon and is based upon the one that preceded it in 

 time. Each stage of growth is therefore the stage that preceded it 



