Chap. II. 



Maimer of Development. 



37 



more strictly under our present head of reversion. Certain 

 structures, regularly occurring in the lower members of the group 



Bymmetrioally on the braast ; and 

 more especially from one case, iu 

 . which a ^jingle eBSciiut mamma 

 ooourrel in the inguinal region of 

 a woman, the daughter of another 

 woman with supernumerary mam- 

 mcB. But I now find (see, for in- 

 stance. Prof. Preyer, 'Der Kampf 

 urn das Dasein,' 1859, s. tS) that 

 tnammae erraticre occur in other 

 situations, as on the back, in the 

 armpit, and on the thigh ; the 

 mammsB in this latter instance 

 having given so much milk that the 

 child was thus nourished. The pro- 

 bability that the additional mammsa 

 are due to reversion is thus much 

 weakened ; nevertheless it still 

 seems to me probable, because two 

 pairs are often found symmetrically 

 on the breast ; and of this I myself 

 have received information in several 

 cases. It is well kjiown that some 

 Lemurs normally have two pairs of 

 maminie on the breast. Five cases 

 have been recorded of the presence 

 of more than a pair of mammae (of 

 course rudimentary) in the male 

 sei of mankind ; see ' Journal of 

 Anat. and Physiology,' 1872, p. 56, 

 for a case given by Dr. Handyside, 

 in which two brothers exhibited 

 this peculiarity ; see also a paper 

 by Dr. Bartels in ' Rc^iciiert's and du 

 Bois-Reyraond's Archiv.,' 1872, p. 

 304. In one of the cases alluded to 

 by Dr. Bartels, a man bore five 

 mammae, one being medial and 

 placed above the navel ; Meckel 

 von Ilemsbach thinks that this 

 latter case is illustrated by a 

 medial mamma occurring in certain 

 Cheiroptera. On the whole we may 

 well doubt if additional mammiB 

 would ever have been developed in 

 both sexes of mankind, had not his 

 enrly progenitors been provided 

 with more than a single pair. 

 In the above work (vol. ii. p. 12), 



I also attributed, though with much 

 hesitation, the frequent cases oi 

 polydactyli.sm in men and various 

 animals to reversion. I was partly 

 led to this through Prof. Owen's 

 statement, that some of the Ich- 

 thyopterygia possess more than five 

 digits, and therefore, as I supposed, 

 had retained a primordial condition; 

 bat Prof Gegenbaur (' Jenaischen 

 Zeitschrift,' B. v. Heft 3, d. 341), 

 disputes Owen's conclusion. On the 

 other hand, according to the opin- 

 ion lately advanced by Dr. Giinther, 

 on the paddle of CeratoduB,whieh is 

 provided with articulated bony rays 

 on both sides of a central chain of 

 bones, there seems no great difficulty 

 in admitting thut 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 supernumerary digits might be 

 due to reversion from the fact that 

 such digits, not only are strongly in- 

 herited, but, as I then believed, had 

 the power of regrowth after ampu- 

 tation, like the normal digits of the 

 lower vertebrata. But I have ex- 

 plained in the Second Edition of my 

 Variation under Domestication why 

 I now plrtce little reliance on the 

 recorded eases of such regrowth. 

 Nevertheless it deserves notice, in 

 as much as arrested developmeni 

 and reversion are intimately related 

 processes ; that various structures 

 in an embryonic or arrested coii' 

 dition, such as a cleft palate, bifid 

 uterus, &c., are frequently accom- 

 panied by polydaotylism. This has 

 been strongly insisted on by Meckel 

 and Isidore Geoffroy St. Hilaire. 

 But at present it is the safest courtie 

 to give up altogether the idea that 



