192 M KIM STIC VARIATION. [I'-VKT I. 



-e,,eral -.--mentation of the trunk. The same author then argues 



'that th" appearance of supernumerary nipples or mamma' along 



tli.- mammary lines is a reversion to an ancestral condition, and a 



\ en, shewing the places at which mammae an- on this 



. believed to have been placed, definite ordinal numbers being 



raed to each. Against this suggestion may be urged those ob- 



LODS to appeals to the hypothesis of reversion which were men- 

 'tioned in th.- Introduction (Section XII.), but in addition to these 

 there are a number of objections applying specially in the case of 

 mammar) Variation. The view that supernumerary mamma' are 



rsions r>--ts on the frequency and deh'niteness with which they 

 occupy certain positions. But 'though they do occur more often 

 in -oi H e po-ition- than in others they are in no sense limited to 

 the-,- position-, tor they may stand anywhere, at least upon the 

 mammary lines. To justify the view that the positions of super- 

 numerary mammae are definite it is necessary to exclude the cases 

 ,,t hitid nipple, of multi])le nipples on the same breast, and of axil- 

 lary i '\i. -n-ions of the mammie, all which phenomena would then 

 he'look.-d "ii as belonging to a class different from that of actual 

 supernumerary mammae. In the argument referred to, this course 

 i- actually adopted. The acceptance of such a view leads to givat 

 ditHculty.' Foi- example, in Neugebauer's case (see Fig. 2!)), 

 William- consider- that the posterior nipples of the two sides be- 

 lon- to different pairs, and have consequently different homologies, 

 use they -tand at different levels. 



Sueh di-tincti<>n- are. 1 believe, unreal. It is surely impossible 

 t<> suppo-e that the Repetition seen in the udders of the two cows 

 in !' I-: '.'- i- a phenomenon different in the two cases. In the one 

 there are two extra teats in symmetrical positions, equally spaced 

 ..lit from the second teats; in the other there is a third teat on 

 one -id.- and a double second or posterior teat on the other. Surely 

 it j- dear that the double condition of this teat represents an im- 

 p.-rfect pha-e ..f a process perfected on the other side. If further 

 proof were needed it ma\ l>e found in the fact already mentioned, 

 that th" mamma' of the pi;.; and other such animals, may be the 

 -Hue in number .sen mi the two sides, but nevertheless stand 

 quit" irregularly and without any \isih|e arrangement into pairs. 



The existence of these cases in which no order of form or regul- 

 arity can lie traced may seem at first sight' 1o lie an insuperable 

 olijeciion to any attempt at the detection of principles in the ar- 

 rangemenl f the mamma'. There is howeyer the fact that many, 

 and indeed in most forms the majority of individuals do shew an 

 orderly and paired arrangement, and the further fact that of those 

 cases which depart from this, a certain number present appear- 

 ances \\hich suggest that t his depart ure has conic about in a regular 

 \\-.\y. Though the irregular cases remain, something would be 

 j. lined if \\e could comprehend any of the elements on which the 



ilarity depend-. The case "f regularity and symmetry, in a 



