40 TABOO AND GENETICS 



out agency of male sperm) proves that in many- 

 simple forms the female nucleus alone possesses 

 all the essential determiners for a new indi- 

 vidual. Boveri's classic experiment (lo) proved 

 the same thing for the male nucleus. He 

 removed the nuclei from sea-urchin eggs and 

 replaced them with male nuclei. Normal in- 

 dividuals developed. To make things still more 

 certain, he replaced the female nucleus with a 

 male one from a different variety of sea-urchin. 

 The resulting individual exhibited the character- 

 istics of the male nucleus only — none of those 

 of the species represented by the egg. Here, 

 then, was inheritance definitely traced to the 

 nucleus. If this nucleus is a male the characters 

 are those of the male line ; if a female those of 

 the female line, and in sexual reproduction 

 where the two are fused, half and half. 



Yet the fact remained that all efforts to 

 develop the spermatozoon alone (without the 

 agency of any egg material at all) into an 

 individual had signally failed. Conklin (ii) had 

 found out in 1904 and 1905 that the egg cyto- 

 plasm in Ascidians is not only composed of 

 different materials, but that these give rise to 

 definite structures in the embryo later on. So a 

 good many biologists believed, and still believe 

 (12, 13, 14) that the egg is, before fertihzation, a 

 sort of " rough preformation of the future 

 embryo " and that the Mendehan factors in 



