delicate filaments which Spence Bate calls "auditory cilia," and which I
have considered to be olfactory organs, as did Leydig before me,
although I was not aware of it. Thus they form long dense tufts in the
males of many Diastylidae, as Van Beneden also states with regard to
Bodotria, whilst the females only possess them more sparingly. In the
Copepoda, Claus called attention to the difference of the sexes in this
respect. It seems to me, as I may remark in passing, that this stronger
development in the males is greatly in favour of the opinion maintained
by Leydig and myself, as in other cases male animals are not
unfrequently guided by the scent in their pursuit of the ardent females.

Now, in our Tanais, the young males up to the last change of skin
preceding sexual maturity resemble the females, but then they undergo an
important metamorphosis. Amongst other things they lose the moveable
appendages of the mouth even to those which serve for the maintenance of
the respiratory current; their intestine is always found empty, and they
appear only to live for love. But what is most remarkable is, that they
now appear under two different forms. Some (Figure 3) acquire powerful,
long-fingered, and very mobile chelae, and, instead of the single
olfactory filament of the female, have from 12 to 17 of these organs,
which stand two or three together on each joint of the flagellum. The
others (Figure 5) retain the short thick form of the chelae of the
females; but, on the other hand, their antennae (Figure 6) are equipped
with a far greater number of olfactory filaments, which stand in groups
of from five to seven together.

(FIGURE 3. Head of the ordinary form of the male of Tanais dubius (?)
Kr. magnified 90 times. The terminal setae of the second pair of
antennae project between the cheliferous feet.