Summary 



That the germ nuclei 

 are the bearers of the 

 heredity quahties seems 

 to be borne out by 



(1) the phenomenon 

 occuring in cell- 

 division; 



(2) the phenomenon 

 occuring in matur- 

 ation ; 



(3j the phenomenon 

 of fertilization; 



(4) the results of 

 breeding experi- 

 ments; and 



(5) the experiments 

 of Boveri with nu- 

 cleated and non- 

 nucleated sea-ur- 

 chin eggs. He 

 found that non- 



Fig, 28. — Diagram illustrating possible 

 results of sexual fusion: 1, sperm with 

 two chromosomes (AA) ; 2. egg with two 

 chromosomes (BB); 3, fertilized egg con- 

 taining two paternal chromosomes: 4, 

 somatic cell, paternal chromosomes dom- 

 inating: 5 and 6, somatic cells, one 

 paternal and one maternal chromosome 

 dominating; 7. somatic cell, maternal 

 chromosomes dominating. (After Coul- 

 ter). 



nucleated framents of unfertilized sea-urchin ova 

 could be fertilized, but such fragments developed into 

 dwarf but normal larvae. Again, Boveri fertilized the 

 nucleated fragments of sea-urchin ova with sperms 

 from another species, and obtained in a few cases dwarf 

 larvae which showed paternal characters only. He 

 concluded therefore that the nucleus was the exclusive 

 bearer of hereditary qualities. 



Some contradictions, however, remain to be explained: — 



for example: 



(1) Loeb's experiments with unfertilized sea-urchin's eggs. 

 Loeb was able to produce normal larvse from unfertiliz- 

 ed sea-urchin eggs by immersing them in a mixture 

 composed of 50% 10-8n, MgCL and 50% of sea water. 



(2) Delage's experiments with non-nucleated ova of sea- 

 urchins. Delage developed normal larvse from non- 

 nucleated, sea-urchin eggs by fertilizing them with 

 sperms. 



(g)— Heredity of Sex 



Much progress has been made in unravelling the ele- 

 mentary mechanism of sex distribution both by cytological 



141 



