60 THE DESCENT OF MAN 



under our present head, of reversion. Certain structures, 

 regularly occurring in tlie lower members of tlie group to 

 wMch man belongs, occasionally make tbeir appearance 

 in him, though, not found in the normal human embryo; 

 or, if normally present in the human embryo, they become 

 abnormally developed, although in a manner which is nor- 

 mal, in the lower members of the group. These remarks 

 will be rendered clearer by the following illustrations. 



In various mammals the uterus graduates from a double 

 organ, with two distinct orifices and two passages, as in the 

 marsupials, into a single organ, which is in no way double, 

 except from having a slight internal fold, as in the higher 

 apes and man. The rodents exhibit a perfect series of gra- 

 dations between these two extreme states. In all mammals 

 the uterus is developed from two simple primitive tubes, the 

 inferior portions of which form the cornua; and it is, in the 

 words of Dr. Farre, "by the coalescence of the two cornua 

 at their lower extremities that the body of the uterus is 

 formed in man; while in those animals in which no middle 

 portion of body exists the cornua remain un-united. As the 



tion, the frequent cases of polydactylism in men and various animals to rever- 

 sion. I was partly led to this through Prof. Owen's statement, that some of 

 the Ichthyopterygia possess more than five digits, and therefore, as I supposed, 

 had retained a primordial condition ; but Prof. Gegenbaur (' ' Jenaisohen Zeit- 

 sohrift," B. v. Heft 3, s. 341) disputes Owen's conclusion. On the other hand, 

 according to the opinion lately advanced by Dr. Giinther, on the paddle of 

 Oeratodus, which is provided with articulated bony rays on both sides of a cen- 

 tral chain of bones, there seems no great difficulty in admitting that six or more 

 digits on one side, or on both sides, might reappear through reversion. I am 

 informed by Dr. Zouteveen that there is a case on record of a man having 

 twenty -four fingers and twenty -four toes ! I was chiefly led to the conclusion 

 that the presence of superniimerary digits might be due to reversion from the 

 fact that such digits not only are strongly inherited, but, as I then believed, 

 had the power of regrowth after amputation, like the normal digits of the lower 

 vertebrata. But I have explained in the Second Edition of my "Variation 

 under Domestication" why I now place little reliance on the recorded cases of 

 such regrowth. Nevertheless it deserves notice, inasmuch as arrested develop- 

 ment and reversion are intimately related processes ; that various structures in 

 an embryonic or arrested condition, such as a cleft palate, bifid uterus, etc., are 

 frequently accompanied by polydactylism. This has been strongly insisted on 

 by Meckel and Isidore GeofEroy St.-Hilaire. But at present it is the safest 

 course to give up altogether the idea that there is any relation between the 

 development of supernumerary digits and reversion to some lowly organized 

 progenitor of man. 



