coelom which we owe to Goodrich, in all the coelomata the coelom is
primarily the generative cavity, on the walls of which the gametocytes are
situated, and the coelomic ducts are the original genital ducts. In
Vertebrates we find two such ducts in both sexes in the embryo, originally
formed apparently by the splitting of a single duct. In the male one of
these ducts becomes connected with the testis while the other degenerates:
the one which degenerates in the male forms the oviduct in the female,
while the one which is functional in the male degenerates in the female.

Intromittent organs are formed in all sorts of different ways in different
animals. In Elasmobranchs (sharks and skates) they are enlarged portions
of the pelvic fins, and therefore paired. In Lizards they are pouches of
the skin at the sides of the cloacal opening. In Mammals the single penis
is developed from the ventral wall of the cloaca. In Crustacea certain
appendages are used for this function. There are a great many animals,
from jelly-fishes to fishes and frogs, in which fertilisation is external,
and there are no intromittent organs at all.

2. ORGANS FOR, CAPTURING OR HOLDING THE FEMALE: for example, the
thumb-pads of the frog, and a modification of the foot in a water-beetle.
Certain organs on the head and pelvic fins of the Chimaeroid fishes are
believed to be used for this purpose.

3. WEAPONS.--Organs which are employed in combats between males for the
exclusive possession of the females. For example, antlers of stags, horns
of other Ruminants, tusks of elephants, spurs of cocks and Phasiamidae
generally, horns and outgrowths in males of Reptiles and many Beetles,
probably used for this purpose.

4. ALLUREMENTS.--Organs or characters used to attract or excite the