336 PRESENT PROBLEMS IN EVOLUTION AND HEREDITY. 



trausfiLsion of blood in rabbits; he found that the blood did not con- 

 vey with it even the slightest tendency to transfer normal character- 

 istics from one variety to auother. 



Matemat . 



Eaterrial., 



Maternal 



Paternal. . 



Materra! , 



Paternal , . 



Fig. 1. 



/. o., fertilized ovum or embryo, coutaiuiuu luiitenialaud paternal characteristics; H, soma, or adult 

 body, coiitaiiiiug n, s, m, d, v, somatic cells of the various tissues; and G, (jerm cells of the reproductive 

 jilands. 



I. Histogenesis. — Showing the succ«.s.sivi' rise G, and union /. o. of the maternal and paternal 

 germ cells by direct histogenesis. 



II. Pange.xesis. — Showing the tissues of the body iS', contributing to the germ cells G, so that 

 each/. 0. is coiniioscd ot olenitnts from both the somatic and germ cells. 



III. Continuity. — Sh<i\ving the division of the embryo/, o., into somatoplasm, s (from which arise 

 the body cells), and germ plasm, <l (which passes direct to the germ cells), establishing a direct con- 

 tinuity. 



Prof. Brooks, of the Johns Hoi)kins l^uiversity, then contribute and 

 original moditication of paugeuesis in which the functions of the ova and 



