into the scrotum, either completely or partially.
In a few animals, as in the porcupine, the opening is never fully closed,
and the testis remains in the cavity of the body most of the time,
passing out only at certain periods. We also occasionally meet cases
of human beings in which the testes have never descended from their
place in the abdominal cavity, giving the individuals the appearance
of eunuchs. This condition, however, though an abnormal one, does not
in any way interfere with the function of the organs, as those who happen
to possess it often imagine. We have also met with cases in which the
organs were movable, and could readily be pressed up into the abdominal
cavity, through the unclosed inguinal cavity, which afforded them a
passage downward in the process of development.

As before remarked, these peculiarities do not affect the functions
of the organs in any appreciable degree, although they not infrequently
give rise to some apprehension on the part of those subject to them.
The left testicle is sometimes a little smaller than the right, another
fact which is seized upon by quacks as a means of exciting the fears
of young men who have been addicted to bad habits, although the
peculiarity is generally without important significance.

The testicles are connected with the urinary passage by means of two
ducts which terminate near the base of the bladder, at which point they
connect with the urethra. We need not dwell at further length upon the
structure of the testicles, as this subject receives fuller attention
elsewhere.

Human spermatozoa are about 1/600 of an inch in length. Those of
reptiles are very much larger. One of the remarkable features of these
minute elements is their peculiar movements. While alive, the
filamentous tail is in constant action in a manner strongly resembling
the movements of the caudal appendage of a tadpole. This wonderful
property led the earlier observers to believe that they were true
animalcula. But they are not to be regarded as such, though one can
scarcely make himself believe otherwise while watching their lively
evolutions, and apparent volitionary movement from one point to
another.

Spermatozoa originate in the testis as cells, which are filled with
granules. After a time, each granule acquires a long appendage, and
then the cell has become converted into a bundle of small zoosperms.
Development still continues, until finally the thin pellicle on the
outside