218 
GENERAL OBNITHOLOGY. 
of appearance as they present under diflFerent circumstances is mainly seasonal. For birds, 
as a rule, procreate only at particular times of the year, rarely having more than one or 
two broods of young : the functional activity and quiescence of the testes correspond, as the 
enormous swelling of the gland during the breeding season is one of the peculiarities of the 
bird's organ. This may be related to the absence, in birds, of specially formed vesiculeB semi- 
nales, or seminal reservoirs ; though certain contortions and dilatations of the sperm -ducts 
which are to be observed may imperfectly answer to detain the secretion until circumstances 
render it available. The passage of the sperm-duct is along the face of the kidneys, generally 
in company with the ureters ; the opening is by a papilla upon the surface of the uro-genital 
sinus. These papillose terminations of the sperm-ducts are erectile to a degree, and answer the 
purpose of paired penes in those birds which are not provided with better-formed copulatory 
parts. In coitu, the cloacal chambers containing the orifices of the genital ducts are opened, 
and the more or less protruded papillae come in contact or close juxtaposition. In cases in 
which a penis or two penes are developed, the urethral passage is a groove, never a tube, 
though cavernous and even muscular tissue may be developed ; and in any case of such an 
intromittent apparatus, it has cloacal invagination when not operative (see p. 680). These 
organs, in all their variety, are of the sauropsidan, not mammalian, type ; though in some 
respects the structure approaches that seen in the non-placental mammals. No prostate or 
cowperian glands exist in birds. 
The sole office of the testis, or oophoron masculinum, is the secretion of semen, associate 
structures being simply accessory, for the conveyance of that vital substance and its transfer- 
ence to the opposite sex. The seminal fluid itself is merely the vehicle of transport of the 
spermatozoa, in which their activity may be freely exercised in their intuitive struggles to gain 
access to their mates in the ovary. It is literally a " sea of life " in which the minute creatures 
swim in shoals to their destiny, — and their fate in any case is death. If they successfully 
bufiet the waves of fate they iind a watery grave in the ovum at last ; if that haven be not 
reached they simply perish in mid-ocean. The spermatozoa, or seminal animalcules, or male 
Dynamamoebce (figs. 106, 107), are the exact counterparts of ovarian ova, in so far as they are 
single-celled animals of a very low grade of organi- 
zation ; but their activity and intelligence is marvel- 
lous, and still more so is the mysterious attribute 
with which they are endowed of assimilating their 
protoplasmic substance with that of the ovum ; with 
the result that the thus fecundated ovum is capable 
of procreating itself by fission for a period until a 
mass of similar creatures is engendered; from which 
mass is then speedily evolved the complex body of matozoa of sparrow, 
Fig lOG. — Spermatozoa 
of domestic cock, greatly 
magnified ; from Owen, after 
Wagner and Leuckart. 
the Bird. 
The correspondmg female Dynamamoebce greatly magnified ; 
, . . • 1 1 • 1 • 1 1 1 from Owen, after 
(ovarian ova) are simple spherical animalcules, pliys- Wagner and Leuck- 
ically indistinguishable from an ordinary encysted J. mce&a; but the sperma- art. 
tozoa are remarkably distinguished in appearance, furnishing probably the best marked case of 
sexual characters to be found among the Protozoa, to which class of animals they belong. The 
spermatozoa resemble flagellate infusoria or ciliated endothelium cells, though they each have 
but a single whip. They are of extremely minute size, much smaller than their females, and 
filamentous ; more or less thickened and sometimes wavy at their nucleated heads, whence pro- 
trudes an excessively delicate thready tail, endowed with great vibratory energy. They may be 
likened to diminutive attenuated tadpoles, which swim by lashing the tail in the seminal fluid. 
Under the microscope shoals of these curious creatures may be seen swimming in the sea, nosing 
about in search of the ovum, butting their heads in wrong places, backing out and trying again 
in another direction ; with such success that out of myriads a score or so may gain their end. It 
