(13/59. Sir H. Holland 'Medical Notes and Reflections' 3rd edition 1855 page
31.) that diseases, such as hydrocele, necessarily confined to the male sex,
can be transmitted through the female to the grandson. Such cases as these
offer, as was remarked at the commencement of this chapter, the simplest
possible examples of reversion; and they are intelligible on the belief that
characters common to the grandparent and grandchild of the same sex are
present, though latent, in the intermediate parent of the opposite sex.

The subject of latent characters is so important, as we shall see in a future
chapter, that I will give another illustration. Many animals have the right
and left sides of their body 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. (13/60.
See Steenstrup on the 'Obliquity of Flounders' in Annals and Mag. of Nat.
Hist.' May 1865 page 361. I have given an abstract of Malm's explanation of
this wonderful phenomenon in the 'Origin of Species' 6th Edition page 186.) 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 flesus 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
species of Bulimus, and many Achatinellae (13/61. Dr. E. von Martens in
'Annals and Mag. of Nat. Hist.' March 1866 page 209.) are as often sinistral
as dextral. I will give an analogous case in the great articulate kingdom: the
two sides of Verruca (13/62. Darwin 'Balanidae' Ray Soc. 1854 page 499: see
also the appended remarks on the apparently capricious development of the
thoracic limbs on the right and left sides in the higher crustaceans.) are so
wonderfully unlike, that without careful dissection it is extremely difficult