the different species of birds. The two in the same bird are usually of
the same size, though one testicle may be slightly larger than the
other. In a summary of a large number of weights of the testicles of ten
months old cockerels, the average weight was 0.021 pound each. The
average measurements were 2 inches in the major diameter and 1 inch in
the minor diameter. In the cockerel before sexual maturity, which is
denoted by the male bird’s crowing, the testicles are very small. They
resemble, in shape, a navy bean and are yellowish-white in color.
_Structure._—The testicle is surrounded by a thin fibrous capsule,
which, in the mature cock, is very vascular. This capsule sends into the
interior of the gland, septa which form the framework, or supporting
structure. This framework forms the spaces in which are located the
glandular substance. The glandular portion consists of the _tubuli
seminiferi_, which are lined with cubical cells. The framework
supporting these tubules gives passage to arterial branches of the
spermatic artery, which furnish an abundant blood supply; the framework
also supports the veins returning the blood from the testicle. The
seminiferous tubules end in blind extremities in the epididymus or
globus minor, and unite in the seminiferous canals. All arteries, veins,
lymphatics, and seminiferous tubules enter or leave through the globus
minor at the attached portion of the testicle. The _epididymis_ is made
up largely of convoluted tubules which are the continuation of the
secreting tubules of the globus major. The walls of the tubules of the
globus minor become thicker and are provided with smooth muscle cells in
addition to the connective tissue and endothelial lining. The convoluted
tubules empty into the vas deferens. The epididymus is covered by the
fibrous capsule; which corresponds to the tunica albuginea of mammals
and may be considered as a reflection or modification of the visceral
peritoneum.
The substance of the testicle is very soft; in fact, it may be said to
be of the consistency of encephaloid material. It is made up of
secreting tubules in which are found the spermatozoa; it also contains
cells which produce an internal secretion, or hormone. There is also
produced some fluid in which the spermatozoa float, the whole material
manufactured constituting the semen.
The _spermatozoa_ of the fowl are provided with long cylindrical bodies,
which may be straight or wavy (Fig. 55, _A_). The body of the
spermatozoon is obtuse anteriorly, and posteriorly, tapers into a
filimentary tail, or flagellum, of varying length, by the aid of which
the spermatozoon moves about in the fluid.
The histological structure of the testicles of the baby chick at
hatching is approximately one-half white fibrous connective tissue. The
seminal tubules are small and widely distributed among the connective
tissue. The cells of these tubules possess rather large nuclei, round in
shape, with linin network and chromatin granules, typical of resting
germ cells. As the bird develops the testicles grow, the seminal tubules
become larger, and the amount of connective tissue correspondingly less.
[Illustration:
FIG. 55.
_A._ Spermatozoa of a cock. _a_, The spermatozoa. _b_, The head. _c_,
The tail.
_B._ The oviduct of a hen removed. _A_, The oviduct. _B_, The superior
ligament. _C_, The inferior ligament. Note the oviduct thrown in
folds and the anastomosing blood-vessels.
]
In addition to the tubules, the spermatogenic cells, and the connective
tissue, there is also in the testicles more or less fat. There is a
small amount of connective tissue between the seminiferous tubules, in
which locations there are also clusters of polyhedral cells, with round
nuclei, others are the interstitial cells.
=The Vas Deferens= (Fig. 54, _D_). _Location and Shape._—Extending from
the epididymus, is the vas deferens which runs backward on the
infero-internal surface of the kidney and to the outside of the ureter.
It is very tortuous passing on the infero-lateral surface of the kidney
in company with the ureter and becoming somewhat expanded posteriorly it
terminates in the upper wall of the cloaca in a rather small papilla
located in the uro-genital portion of the cloaca anterior to the mouth
of the ureter. This papilla is the organ of copulation and in ducks is
very large, and spirally elongated, and retractile forming a kind of
penis. The papilla is traversed by a furrow on the upper surface through
which the semen flows.
_Structure._—The vas deferens is covered and supported by the
peritoneum. Its wall is made up of a fibrous structure in which may be
found smooth muscle fibers. The wall does not possess glands. It is
lined with columnar epithelium. The posterior end is expanded and
terminates into a papilla. The base of the papilla is surrounded by a
plexus of arteries and veins, which serve as an erectile organ during
the venereal orgasm, when the fossa of the turgid papilla is everted,
and the semen brought into contact with the similarly everted orifice of
the oviduct of the female, along which the spermatozoa pass by
undulatory movements of their ciliary appendage, or tail.
THE FEMALE GENERATIVE ORGANS (Fig. 56)
The female generative organs consist of one ovary and an oviduct.
_Location._—The ovary is located similarly to the testicles of the male
bird, in the sublumbar region of the abdominal cavity, just at the
anterior end of the kidneys, posterior to the lungs, and slightly to the
left of the center.
_Shape._—In the pullet the ovarian mass appears somewhat like a bunch of
grapes, being made up of from 3500 to 4500 small, whitish spheres, which
represent the undeveloped ova, and which in the active state are
developed, one by one, into yolks with their blastoderms. From the
blastoderm the fetus may later be developed. In the active ovary of the
laying hen the ovarian mass is of considerable size, as it contains ova
in different stages of development. Only one ovum is completely
developed at a time, though occasionally there may be only a few hours
between the maturity of successive ova. The ova receives nourishment
from the blood-vessels of the capsule, which vessels are branches of the
ovarian artery.
[Illustration:
FIG. 56.—Functionating female generative organs of a hen. 1, Ova in
process of formation of yolk. 2, Stigmal line at which point the
capsule ruptures when ovum is mature. 3, The funnel end of the
oviduct. 4, The oviduct torn loose and laid to one side, the
albumin-secreting portion. 5, The shell membrane secreting portion.
6, The albumin. 7, The yolk. 8, The shell-secreting portion. 9, The
cloaca. 10, The rectum.
]
_Structure._—The ovary contains very vascular cellulofibrous tissue. The
ovum as it develops is attached to the ovarian body by means of a
delicate white fibrous pedicle. When the yolk is mature it escapes from
the enveloping fibrous capsule by a cleavage of the capsule. The
cleavage line is called the _stigmen_ (Fig. 56, No. 2). The yolk is
surrounded by a very delicate membrane called the _vitelline membrane_.
The empty sac now shrinks and finally disappears.
=The Egg.=—The principal divisions of the egg are the yolk, the albumin
outside of the yolk content, the shell membranes and the shell (Fig.
58). As stated, the _yolk_ is formed in the ovary, leaving the other
three portions to be formed in the oviduct.
[Illustration:
FIG. 57.—Section through the ovary of the hen. _a_, The ova. _d_, An
ovum beginning to receive deposits of yolk material. _c_, Ova
farther advanced in yolk formation.
]
The _albumin_ may be subdivided into, first, a thin layer of albumin
lying close around the yolk; second, a thick layer of albumin lying at
the outer periphery; and third, a modification of the albumin called the
chalazæ. The chalazæ are twisted, dense cord-like structures at either
pole of the yolk, one end of which is adherent to the vitelline membrane
and the other to the inner membrane surrounding the albumin. The chalazæ
thus act as stays to this structure, which is carrying a delicate
burden, the blastoderm.
The _shell membrane_ consists of two layers, an inner delicate, and an
outer thicker layer. When the egg is just laid these two membranes are
in all parts closely adherent to each other, and the egg content
completely fills the shell cavity. As soon as the content cools there is
a slight contraction; the two shell membranes separate at the large end
of the egg, forming an air cell which gradually enlarges as the
evaporation of liquid through the pores of the shell takes place.
[Illustration:
FIG. 58.—A diagram of the parts of the egg. _a_, The blastoderm. _b_,
The shell. _c_, The outer shell membrane. _d_, The inner shell
membrane. _e_, The air-sac at the large end of the egg. _f_, The
albumin. _g_, The chalaza. _h_, The yellow layers of yolk. _i_, The
white layers of yolk. _k_, The flask-shaped portion of white yolk.
_l_, The vitelline membrane.
]
The shell consists of several layers. Three are easily distinguishable:
first, an inner mammillary layer, consisting of minute conical deposits
of calcareous material; second, a middle spongy layer, composed of a
thick network of fibers; third, an outer delicate, cuticle-like
structure. In certain breeds of poultry a pigment may be added; for
example, in ducks a pea green, in turkeys a spotted brownish material,
and in fowls pink and various shades of brown. The egg shell is porous
to admit the free exchange of air during the process of incubation.
An average sized hen egg weighs about 2 ounces, of which 11 per cent. is
shell, 32 per cent. yolk, and 57 per cent. white. The principal chemical
constituents of the egg are as follows: ash, or mineral matter, 9 per
cent.; fat, or hydrocarbon, 9.3 per cent.; proteids, or nitrogenous
matter, 11.9 per cent.; and water, 65.5 per cent. There is apparently no
constant proportion of weight between the yolk and albumin. There is
also a variation in the weight of the shell due to its variation in
thickness.
In an examination of ten eggs of average size, the yolk constituted 31
per cent. of the total weight of the egg.
The following is the result of the analysis of twelve eggs of average
size. This analysis included the shell and all other parts taken
together.[6]
Footnote 6:
The analysis was made by D. M. McCarty, chemist, Animal Industry
Division, North Carolina Experiment Station.
Moisture 64.25 per cent.
Dry matter 35.75 per cent.
————————————————
100.00 per cent.
Parts per hundred including
shell
Protein 10.2500
Fat 10.6200
Phosphorus .3020
Calcium .6080
Magnesium .0985
Iron .0103
Sulphur .3950
Chlorine .1506
Potassium .0103
Sodium .2000
=The Oviduct.=—The three separate and distinct portions of the egg,
albumin, shell membranes, and the shell, are constructed in different
parts of the oviduct.
_Location._—The oviduct of the hen extends along the left side of the
bodies of the vertebræ, and the roof of the pelvic cavity and lies
dorsal to the abdominal air-sac. It extends from the posterior border of
the ovary and empties into the cloaca (Fig. 56, No. 3 and 8) through a
transverse slit.
_Shape._—In a well-developed Plymouth Rock pullet, but one whose
reproductive organs have never become active, the oviduct is about 4½
inches long; in the fully developed and active state it is from 18 to 20
inches long, and in a collapsed state about ½ inch in diameter. It is
held in position by two ligaments, a dorsal and a ventral (Fig. 55, _B_)
to be described later. The oviduct is tortuous in its course, forming
three principle convolutions before reaching the cloaca, and like the
ovarian mass, in its active state, pushes the abdominal viscera downward
and toward the right side.
_Structure._—The oviduct consists of three coats: first, the serous,
located on the outside, which is a reflection of the peritoneum; second,
the muscular middle tunic; third, the mucous coat, which in a resting
state is thrown into folds.
[Illustration:
FIG. 59.—The active oviduct of a hen laid open. 1, The ovary. 2, The
funnel. 3, The albumin-secreting portion. 4, The isthmus. 5, The
shell=gland portion. 6, The vagina. 7, The superior ligament. 8, The
inferior ligament.
]
=Parts of the Oviduct.=—The parts of the oviduct are as follows: the
funnel, the albumin-secreting portion, the isthmus, the shell-gland
portion, or uterus, and the vagina (Fig. 59).
[Illustration:
FIG. 60.—The mucous lining of the oviduct.
_A._ Transverse section of the oviduct wall in the region of the neck
of the funnel showing primary and secondary folding of the
epithelium (after Surface).
_B._ Showing the type of gland cells of the funnel region.
_C._ Transverse section through the wall of the uterus showing the
deep folds.
_D._ Section from the albumin-secreting portion showing the opening of
a tubular gland and also showing the character of the cells.
]
The _funnel_ is the trumpet-shaped portion, the ostium tubæ abdominale,
whose mouth or fimbriated opening faces the ovary, and lies ventrally to
receive the ovum, or yolk, as it is discharged from the ovary. Its thin
wall, expanded in the anterior portion, is provided with fimbriæ-like
projections. This funnel-shaped portion soon converges to form a
constricted portion. This portion of the active oviduct is from 3 to 4
centimeters long. The mucous membrane occurs in folds forming low
longitudinal spiral ridges (Fig. 60, _A_). The fimbriæ are continuous
with the dorsal and the ventral ligament of the oviduct; and from this
point, where the ridges of the mucous membrane are almost nil, they
gradually increase in height as they extend down the tube. These ridges
are continued in those of the second, or albumin-secreting portion (Fig.
60, _D_). At this point they increase in height very rapidly. Here the
bundles of muscular fibers of the middle coat are thin and distributed
among bundles of connective tissue. The muscular fibers consist of two
layers, an outer longitudinal and an inner circular. At places in this
portion the inner bundles may be noted to extend longitudinally. In
embryological development the epithelial layer has an origin different
from the outer layers of the oviduct. In the fetal development the
Müllerian duct arises as a thickening along the Wolffian body just
ventral to the gonad. This Müllerian duct is at first a solid cord of
cells. It later develops a lumen, and grows posteriorly until it
connects with the cloaca. At the time of this posterior growth,
mesenchyme cells migrate in from the surrounding tissue and form a layer
about the duct. From this layer of mesenchyme cells there are developed
the outer layers of the oviduct, which layers later develop the muscular
structure and the connective tissue. The epithelium and its derivatives,
which represent the glandular structures, are formed from the walls of
the old Müllerian duct. Thus the two sets of tissues, having different
origins, likewise have different functions. The epithelium is concerned
entirely with secretion, and the derivatives of the mesenchyme are
concerned with supporting and muscular function.
[Illustration:
FIG. 60. _A._—The mucous lining of the oviduct.
_E._ Section of the epithelium from the vagina showing unicellular
glands.
_F._ A section from the isthmus showing opening of a tubule.
]
To summarize, six layers of tissue occur in the funnel region, namely,
an outer serous covering, an outer longitudinal muscular layer, a layer
of connective tissue, an inner circular layer, a second layer of
connective tissue, and an inner mucous layer. The mucous layer is made
up of glands, as follows. The unicellular glands occur between the
ciliated cells of the epithelium. These glands are found only in the
posterior half of this division of the oviduct. The glandular grooves
are made up of an accumulation of gland cells at the bottom of the
grooves between the secondary folds of the epithelium. These are found
in all parts of this division except the extreme posterior part. In the
posterior part we find the third type of glands, the tubular variety.
The second division of the oviduct, as stated above, is the
_albumin-secreting portion_. The funnel division gradually merges into
the second portion. These two portions are distinguishable from each
other. The walls of the albumin-secreting portion are much thicker and
the longitudinal ridges are higher. This section is the longest of the
five divisions, measuring from 40 to 42 centimeters in length, or more
than half the length of the oviduct. The albumin division terminates
rather abruptly into the third division, the isthmus (Fig. 59, _A_).
It is probable that the secretion of albumin is not confined to the
cells of the second division; yet we are safe in saying that the major
portion is formed here. The folds of mucous membrane in this division
are thicker and higher than in the funnel, due to their containing cells
of the high columnar type, and to the fuller development of the glands
which are of the tubular variety. The muscular layer is heavier, and
therefore the muscular power to force along the tubes’ contents is
greater. In the formation of the mucous folds we find, in transverse
sections, that the central core is made up of connective tissue which
carries blood-vessels and nerve filaments, as in other similar glandular
structure. The epithelium contains glandular cells of two varieties,
namely, the ciliated, columnar variety, and the unicellular, goblet
variety (Fig. 36, No. _B_, 2). These two kinds of glandular cells are
rather evenly distributed throughout the epithelium of this section of
the oviduct. The unicellular gland cells are more numerous at the mouths
of the ducts leading from the tubular glands. The nuclei of the ciliated
cells are oval and lie near the middle of the cells or a trifle toward
the base from the middle. The protoplasm of the cells is finely
granular. Strong cilia in considerable number surmount each cell. In
some cases the goblet or mucous cells have pushed apart the ciliated
cells, and their prolongations extend farther than the surface of the
ciliated cells. The nuclei of the goblet cells are round, and lie nearer
the proximal end than those of the ciliated cells.
The third division of the oviduct, the _isthmus_, continues from the
albumin-secreting portion and terminates in the expanded portion called
by some anatomists, the uterus. Toward the posterior end of the
albumin-secreting portion the longitudinal folds of mucous membrane
become lower, making, at the juncture of this and the isthmus, a clear
fine of demarcation. For a distance of 2 or 3 centimeters the folds are
low, after which they gradually become higher, but never reach the
height or thickness of those in the albumin-secreting portion.
The clear-cut line between the albumin-secreting portion and the isthmus
is partly due to a zone in which the long tubular glands are lacking.
The core of the folds of mucous membrane in this zone contain much more
connective tissue. The cells are both ciliated and unicellular. The rest
of the histological structure of the isthmus is the same as that of the
albumin-secreting portion.
The function of the isthmus is to secrete, or to form, the shell
membrane, the membrana testacea.
The fourth division of the oviduct is the _uterus_, or the shell-gland
portion (Fig. 60, _C_). There is no clear line of demarcation between
the isthmus and shell-gland portion, the walls gradually expanding. In
this region the folds of mucous membrane become leaf-like and of
considerable length, extending into the lumen, thus affording a greater
cellular surface. The same coats of the duct are present here as in
other parts; but the outer longitudinal muscular layer is thicker and
possesses more strength. The quantity of connective tissue is about the
same. The glands are of a tubular type and the same two varieties of
epithelial cells are found here as elsewhere, namely, the ciliated high
columnar and the unicellular mucous variety.
In the active glandular cells of the shell-forming region the nuclei are
small, dark staining, and lie toward the center of the cell. The
chromatin granules and nucleoli take on a comparatively deep basic
stain, but they do not show the intense stain found in the albumin and
the isthmus region. The cytoplasm of the uterine tubular glands does not
present as heavy a granular appearance as that of the albumin portion.
These cells are diffusely granular, the granules appearing of one size
and taking the stain faintly. The function of this portion is to
secrete, or form, the hard calcareous covering which has been described
at the beginning of this section.
The fifth division of the oviduct is the _vagina_. There is located, at
the juncture of the shell-gland portion with the vagina, a strong
sphincter muscle. The vagina is that constricted portion of the oviduct
extending from this muscle to the cloaca. The mucous membrane forms low
narrow folds with secondary folds, which appear continuous with those of
the shell-gland portion. The core of these folds is composed of
connective tissue. The vagina in the hen of average size measures from
12 to 13 centimeters long (Surface). The inner or circular muscular
layer is well developed; it is much thicker than in any other part of
the oviduct. This extra development gives the power necessary to
successfully expel the egg. The outer longitudinal layer is not so well
developed; its bundles are scattered throughout the connective-tissue
layers. The egg is caused to move along in the oviduct by a successive
series of contractions of the circular muscular fibers posterior to it.
There are no tubular glands in this portion, but a simple layer of high
ciliated columnar epithelium, and some goblet, or mucous cells. The
cells on the surface generally are long and slender; in the grooves
between the mucous folds the cells are shortest, reaching their greatest
length at the tops of the folds.
The function of the vagina is the secretion, or formation, of the outer
shell cuticle commonly called the bloom, and also in certain breeds, as
indicated above, the tint.
The cloaca furnishes a passage way from the vagina to the external world
by way of the anus. The walls of the cloaca contain glands.
=The Ligaments of the Oviduct.=—It is held in position by two ligaments,
one dorsal and one ventral. The _dorsal ligament_ of the oviduct is
formed by a double layer of peritoneum with a very small amount of
connective tissue interposed. The peritoneum is also reflected over the
oviduct. The ventral ligament of the oviduct is narrower than the
dorsal, but is similarly constructed. Both ligaments are rather
veil-like in appearance. During the first four or five months of the
growth of the young female fowl the development of the oviduct and its
ligaments is in proportion to that of the body. With the elongation that
takes place about the time of functionation, as described above, the
ligaments enlarge in proportion to the enlargements of the oviduct. The
dorsal ligament maintains a line of attachment to the body wall from the
caudal end of the body cavity to the fourth thoracic rib. The ventral
ligament elongates only slightly during this developing period. It
becomes thicker and stronger and early develops a muscular coat. It also
grows in width except at the caudal end. At this point the ligament is
simply a mass of muscular tissue of the smooth or involuntary type.
These ligaments are fan-shaped.
The muscle fibers of the dorsal ligament of the laying hen, have their
origin in a line near the medial side of the dorsal margin. At this
point the bundles of fibers are quite thick, but are spread out thinly
toward the margin of the oviduct. Frequent anastomoses are noted. The
muscular fibers become continuous with the circular ones of the oviduct.