Chap. VIIL] SEXUAL SELECTION. 2?1 



proper to its own male and female sex to the hybrid off- 

 spring of both sexes. The same fact is likewise manifest, 

 when characters proper to the male are occasionally de- 

 veloped in the female Avhen she grows old or becomes 

 diseased; and so conversely with the male. Again, char- 

 acters occasionally appear, as if transferred from the male 

 to the female, as when, in certain breeds of the fowl, spiirs 

 regularly appear in the young and healthy females ; but 

 in truth they arc simply developed in the female ; for in 

 every breed each detail in the structure of the spur is 

 transmitted through the female to her male olFspring. In 

 all cases of reversion, characters are transmitted through 

 two, three, or many generations, and are then under cer- 

 tain unknown favorable conditions developed. This im- 

 portant distinction between transmission and development 

 will be easiest kept in mind by the aid of the hypothesis 

 of pangenesis, whether or not it be accepted as true. Ac- 

 cording to this hypothesis, every unit or cell of the body 

 throws off gemmules or undeveloped atoms, which are 

 transmitted to the offspring of both sexes, and are multi- 

 plied by self-division. They may remain undeveloped 

 durmg the early years of life or during successive genera- 

 tions ; their development into units or cells, like those 

 from which they were derived, depending on their affinity 

 for, and union with, other units or cells previously devel- 

 oped in the due order of growtli. 



Inheritance at Corresponding Periods of Life. — This 

 tendency is well established. If a new character appears 

 in an animal while young, whether it endures throughout 

 life or lasts only for a time, it will reappear, as a general 

 rule, at the same age and in the same manner in the off- 

 spring. If, on the other hand, a new character appears at 

 maturity, or even during old age, it tends to reappear in 

 the offspring at the same advanced age. When deviations 



