28 INHERITANCE. Chap. XIII. 



unequally developed : this is well known to be the case with 

 flat-fish, in which the one side differs in thickness and colour 

 and in the shape of the fins, from the other, and during the 

 growth of the young fish one eye is gradually twisted from 

 the lower to the upper surface. 60 In most flat-fishes the left 

 is the blind side, but in some it is the right ; though in both 

 cases reversed or" wrong fishes," are occasionally developed ; 

 and in Platessa flcsus the right or left side is indifferently the 

 upper one. With gasteropods or shell-fish, the right and left 

 sides are extremely unlike ; the far greater number of species 

 are dextral, with rare and occasional reversals of development, 

 and some few are normally sinistral ; but certain sjaecies of 

 Bulimus, and many Achatinella?, 61 are as often sinistral as 

 dextral. I will give an analogous case in the great articulate 

 kingdom : the two sides of Verruca 62 are so wonderfully 

 unlike, that without careful dissection it is extremely difficult 

 to recognise the corresponding parts on the opposite sides of 

 the body ; yet it is apparently a mere matter of chance 

 whether it be the right or the left side that undergoes so 

 singular amount of change. One plant is known to me 63 in 

 which the flower, according as it stands on the one or other 

 side of the spike, is unequally developed. In all the foregoing 

 cases the two sides are perfectly symmetrical at an early 

 period of growth. Now, whenever a species is as liable to be 

 unequally developed on the one as on the other side, we may 

 infer that the capacity for such development is present, 

 though latent, in the undeveloped side. And as a reversal of 

 development occasionally occurs in animals of many kinds, 

 this latent capacity is probably very common. 



The best yet simplest cases of characters lying dormant 

 are, perhaps, those previously given, in which chickens and 

 young pigeons, raised from a cross between differently coloured 



60 See Steenstrup on the ' Obliquity p. 209. 



of Flounders' : in ' Annals and Mag. of 62 Darwin, ' Balanitis?,' Ray Soc, 



Nat. Hist.' May, 1865, p. 361. I 1854, p. 499 : see also the appended 



have given an abstract of Malm's remarks on the apparently capricious 



explanation of this wonderful pheno- development of the thoracic limbs on 



menon in the ' Origin of Species' 6th the right and left sides in the higher 



Edit. p. 186. crustaceans. 



61 Dr. E. von Martens, in ' Annals ei Mormodes ignea : Darwin, ' Fer- 

 nnd Mag. of Nat. Hist.' March, 1866, tilisation of Orchids,' 1862, p. 251. 



