ng.

(2) There were occasionally two pairs of ovaries, each with its
own oviduct; the external apertures of these varied in position,
being upon segments 13 and 14, 14 and 15, or 15 and 16.
Occasionally when there was only the normal single oviduct pore
present it varied in position, once occurring on the 10th, and
once on the 11th segment.

(3) The male generative pores varied in position from segments
14 to 20. In one instance there were two pairs instead of the
normal single pair, and in this case each of the four apertures
had its own prostate gland.

Mr. Beddard remarks that all, or nearly all, the above variations are
found _normally_ in other genera and species.

When we consider the enormous number of earthworms and the comparatively
very small number of individuals examined, we may be sure, not only that
such variations as these occur with considerable frequency, but also
that still more extraordinary deviations from the normal structure may
often exist.

The next example is taken from Mr. Darwin's unpublished MSS.

"In some species of Shrews (Sorex) and in some field-mice
(Arvicola), the Rev. L. Jenyns (_Ann. Nat. Hist._, vol. vii. pp.
267, 272) found the proportional length of the intestinal canal
to vary considerably. He found the same variability in the
number of the caudal vertebrae. In three specimens of an
Arvicola he found the gall-bladder having a very different
degree of development, and there is reason to believe it is
sometimes absent. Professor Owen has shown that this is the case
with the gall-bladder of the giraffe."

Dr. Crisp (_Proc. Zool. Soc._, 1862, p. 137) found the gall-bladder
present in some specimens of Cervus superciliaris while absent in
others; and he found it to be absent in three giraffes which he
dissected. A double gall-bladder was found in a sheep, and in a small
mammal preserved in the Hunterian Museum there are three distinct
gall-bladders.

The length of the alimentary canal varies greatly. In three adult
giraffes described by Professor Owen it was from 124 to 136 feet long;
one dissected in France had this canal 211 feet long; while Dr. Crisp
measured one of the extraordinary length of 254 feet, and similar
variations are recorded in other animals.[22]

The number of ribs varies in many animals. Mr. St. George Mivart says:
"In the highest forms of the Primates, the number of true ri