PERIOD AT WHICH CHARACTERS APPEAR. 217 
inheritance with the two very important laws of homotopic 
and contemporaneous transmission by inheritance. We 
understand by them the fact that changes acquired by an 
organism during its life, and transmitted to its descendants, 
appear in the same part of the body in which the parental 
organism was first affected by them, and that they also 
appear in the offspring at the same age as that at which 
they did so in the parent. 
The law of contemporaneous or homochronous transmis- 
sion, which Darwin ealls the law of “ transmission in 
corresponding periods of life,” can be shown very clearly 
in the transmission of diseases, especially of such as are 
recognized as very destructive, on account of their here- 
ditary character. They generally appear in the organism 
of the child at the time corresponding with that in which 
the parental organism contracted the disease. Hereditary 
diseases of the lungs, liver, teeth, brain, skin, etc., usually 
appear in the descendants at the same period, or a little 
earlier than they showed themselves in the parental organ- 
ism, or were contracted by it. The calf gets its horns at 
the same period of life as its parents did. In like manner 
the young stag receives its antlers at the same period of life 
in which they appeared in its father or grandfather. In 
every one of the different sorts of vine the grapes ripen at 
the same time as they did in the case of their progenitors. 
It is well known that the time of ripening varies greatly in 
the different sorts ; but as all are descended from a single 
species, this variation has been acquired by the progenitors 
of the several sorts, ‘and has then been transmitted by 
inheritance. 
The law of homotopic transmission, which is most 
