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Show lG I~ITERITANCE. CHAP. XII. fi h t Off they arc perfectly reproduced in about six weeks' water s are cu ' < time. 1 l facts we may infer that supernumerary From t 1ese severa · d' . . . t . t certain extent an embryomc con 1- digrts m man re am o a l d' 't tw. n and that t h ey r.e semb le in this respect the norma rgbr l s d'l. b ·n the lower vertebrate classes. They also resem e an rm s l · h b eeding 1- d' 't f some of the lower animals m t e num er exc tL1e 1g1 S 0 · h'b' ( l fi £ ammal bird existin~r reptrle, or amp l ran un ess ve · or no m ' ' u d h 'll the 't u b ere l e on the hr' nd feet of the toad an ot er tarh 'els s Batrachians be viewed as a digit) has more than five; w l st :fishes sometimes have in their pectoral fins as ma~y as twenty metacarpal and phalangeal bones, whi~~' to~ether ';'Ith t?e bony filaments, apparently represent our chgits With their narls. ~o, . r'n cer·tain extinct reptiles, namely, the Ichthyopterygia, ao-am, < • 'fi t "L'Jthe digits may be seven, eight, or nine in number, a sigm can mark," says Professor Owen, "of ~iscine affi.r~ity." 39 vVe encounter much difficulty m attemptmg to reduce these varw· us 1r ac ts to a11y rule or law · The inconstant nu·m ber ho f the adu.itional digits--their irregular attachment. to e1t~1er t e I-nner or ou ter· mar·oa in of the hand-the grada. tiOn wl. uc. h can be traced from a mere loose rudiment of a smgle d1grt to ~ completely double hand-the occasional ~ppearance of additional digits in the salamander after. a .hmb has been am~utated- these various facts appear to mdwate mere fluctuatJ~g monstrosity; and this perhaps is all that ~an be ~afely sard. Nevertheless, as supernumerary digits in the higher ammals, f:om their power of rearowth and from the number thus acqmred exceeding five, pa~take of the nature of the digits in the lower vertebrate animals ;-as they occur by no means rarely, and are transmitted with remarkable strength, though perha~s not ~ore strongly than some other anomalies ;-and as wr~h. ammals which have fewer than five digits, when an addrtwna~ ?ne appears it is generally due to the development of a. VJsrble rudiment ;-we are led in all cases to suspect, that, although no actual rudiment can be detected, yet that a latent tendency .to the formation of an additional digit exists in all mammals, mcluding man. On this view, as we shall more plainly see in the 39 • On the Anatomy of Vertebrates,' 18G6, p. 170: with respect to the pectoral fins of fishcil, pp. 16G-1G8. CHAP. XII. INHERITANCE. 17 next chapter when discussing latent tendencies, we should have to look at. the whole case as one of reversion to an enormously remote, lowly-organised, and multidigitate progenitor. I may here allude to a class of facts closely allied to, but somewhat different from, ordinary cases of :inheritance. Sir H. Holland 40 states that brothers and sisters of the same family are frequently affected, often at about the same age, by the same peculiar disease, not known to have previously occurred in the family. He specifies the occurrence of diabetes in three brothers under ten years old; he also remarks that children of the same family often exhibit in common infantile diseases the same peculiar symptoms. My father mentioned to me the case of four brothers who died between the ages of sixty and seventy, in the same highly peculiar comatose state. An instance has been already given of supernumerary digits appearing in four children out of six in a previously unaffected family. Dr. Devay states41 that two brothers married two sisters, their firstcousins, none of the four nor any relation being an albino; bnt the seven children produced from this double marriage were all perfect albinoes. Some of these cases, as Mr. Sedgwick 42 bas shown, are probably the result of reversion to a remote ancestor, of whom no record had been preserved; and all these cases are so far directly connected with inheritance that no doubt the children inherited a similar constitution from their parents, and, from being exposed to nearly similar conditions of life, it is not surprising that they should be affected in the same manner and at the same period of life. Most of the facts hitherto given have served to illustrate the force of inheritance, but we must now consider cases, grouped as well as the subject all~s into classes, showing how feeble, capricious, or deficient the power of inheritance sometimes is. When a new peculiarity first appears, we can never predict whether it will be inherited. If both parents from their birth present 4° 'Medical Notes and Reflections,' 1839, pp. 24, 34. See, also, Dr. P. Lucas, 'l'Hered. Nat.,' tom. ii. p. 33. 41 'Du Danger des Maringes Con- VOL. II. sanguins,' 2nJ erlit., 1862, p. 103. 42 ' British and Foreign MedicoChirurg. Review,' July, 1863, pp. 183, 189. c |
