Vasa deferentia open separately in segment 18, each furnished at its termination with a large prostate gland.
Between two and three hundred specimens were examined, and among them thirteen specimens exhibited the following marked variations:—
(1) The number of the spermathecae varied from two to three or four pairs, their position also varying.
(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 Darwin's unpublished MSS.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.