Nevertheless there is reason to believe that with all hermaphrodites two individuals, either occasionally or habitually, concur for the reproduction of their kind.
This view was long ago doubtfully suggested by Sprengel, Knight and Kolreuter.

We shall presently see its importance; but I must here treat the subject with extreme brevity, though I have the materials prepared for an ample discussion.

All vertebrate animals, all insects and some other large groups of animals, pair for each birth.

Modern research has much diminished the number of supposed hermaphrodites and of real hermaphrodites a large number pair; that is, two individuals regularly unite for reproduction, which is all that concerns us.

But still there are many hermaphrodite animals which certainly do not habitually pair, and a vast majority of plants are hermaphrodites.