278 THE PRINCIPLES OF [Part II. 



There are, moreover, many animals, in which the two 

 sexes closely resemble each other, and yet both differ 

 from their young ; and here the characters of the adults 

 must have been acquired late in life ; nevertheless, these 

 characters in apparent contradiction to our rule, are trans- 

 ferred to both sexes. We must L not, however, overlook 

 the possibility or even probability of successive variations 

 of the same nature sometimes occurring, under exposure 

 to similar conditions, simultaneously in both sexes at a 

 rather late period of life ; and in this case the variations 

 would be transferred to the offspring of both sexes at a 

 corresponding late age ; and there would be no real con- 

 tradiction to our rule of the variations which occur late in 

 life being transferred exclusively to the sex in which they 

 first appeared. This latter rule seems to hold true more 

 generally than the second rule, namely, that variations 

 which occur in either sex early in life tend to be trans- 

 ferred to both sexes. As it was obviously impossible even 

 to estimate in how large a number of cases throughout the 

 animal kingdom these two propositions hold good, it oc- 

 curred to me to investigate some striking or crucial in- 

 stances, ahd to rely on the result. 



An excellent case for investigation is afforded by the 

 Deer Family. In all the species, excepting one, the horns 

 are developed in the male alone, though certainly trans- 

 mitted through the female, and capable of occasional ab- 

 normal development in her. In the reindeer, on the other 

 hand, the female is provided with horns ; so that in this 

 species, the horns ought, according to our rule, to appear 

 early in life, long before the two sexes had arrived at 

 maturity and had come to differ much in constitution. In 

 all the other species of deer the horns ought to appear 

 later in life, leading to their development in that sex 

 alone, in which they first appeared in the progenitor of 

 the whole Family. Now, in seven species, belonging to 



