ORIGIN AND DEVELOPMENT 43 



16. It is remarkable that both the ova and 

 the spermatozoa appear in the same part 

 of the early embryo, a layer of germinal 

 matter, which is cut off, at an early period, 

 from the matter that is to form the body of 

 the individual, whether male or female. The 

 exact origin of the reproductive elements has 

 not been clearly established. It is suggestive 

 that immature ova are found in the ovary of 

 a female long before birth. There they lie 

 dormant, or undergo very slow changes till 

 puberty. The early origin of spermatozoa 

 has not been clearly established; the cells 

 that produce them are not active till the begin- 

 ning of adolescence. In the female the 

 extrusion of ova continues until perhaps fifty 

 years of age, but the production of sperma- 

 tozoa by the male may last through a long 

 life. Many intricate arrangements for the 

 nutrition and support of both are found in 

 the ovary and testis. Of themselves, at all 

 events in the higher animals, neither male 

 nor female element alone can originate a new 

 individual. The two must unite and blend 

 together This is fecundation. Antecedent 



