The season. At other times, the testes are

The Aves, one of the class for the Chordata
phylum are unisexual vertebrates. The development of the reproductive glands
of the birds are not developed equally in pairs but instead, are found singly.
This adaption tends to decrease the weight of the bird. In the male
reproductive system of the bird, there is a pair of testes which increases in
size in the breeding season. At other times, the testes are smaller in size.
The testes produce sperms and hormones which will be passed into the vasa
efferentia and then to the vans deferens which opens into the seminal vesicle
which will be emptied into the cloaca during mating. As for the female
reproductive system, the female bird tends to have a large, irregular-shaped
ovary attached to the left kidney by the mesovarium. The follicles in the ovary
produces some large and yolky ova which escape into the left oviduct which is
also known as the Mullerian Duct. It is a thick-walled, coiled structure which
secretes albumen and other substances to form shell membranes with calcareous
outer coverings. The posterior end of the oviduct secretes mucus for expelling
the egg. The fertilisation of the egg takes place in the oviduct with the sperm
entry. As the egg passes down, albumen, shell membranes and shell are deposited
on it.

The birds are considered as
amniotes, in which they produce amniotic eggs. In the egg the embryo is
protected and nourished by four extraembryonic membranes which is the amnion,
chorion, yolk sac and allantois. Outside of the amnion will be a calcareous
covering for the birds. Most birds are oviparous, and the eggs are laid in the
nest will be incubated by the warmth of the adult bird’s body. Upon hatching,
the young chick is nourished by fatty secretion produced in the crop of the
parent’s digestive system. During breeding season, the wall of the crop
thickens, and under the influence of the prolactin, it releases a very
nutritious ‘milk’. The chorion layer is the major organ of gaseous exchange in
birds; the amnion plays a role to prevent desiccation of embryo and to act as
the protective cushion which helps the embryo within to absorb shock. The
allantois part help stores the nitrogenous waste in birds and is only
functional in birds. The yolk sac stores food and slowly digest it for use by
the embryo. The first phase of development occurs when the blastoderm of the
eggs started to expand and thicken in which the three germinal layers of the
embryo started to cleavage under the stage of gastrulation and organogenesis.
The fertilized eggs tend to show the presence of the blastoderm within the
yellow yolk, whereas unfertilized egg does not.

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One strength of the chicken
(Gallus gallus domesticus), as a model organism for developmental biology is
that the embryo develops outside the female and is easily accessible for
experimental manipulation. Many techniques allow scientist to examine chicken
embryo inside the eggshell (in vivo) but embryonic access can be limited at
later stage of development. Fortunately, chicks can also be cultured  (ex ovo) or outside the eggshell. The major
advantage to ex ovoculture is greater access to tissues that might otherwise be
obstructed by the shell or the orientation of the chick within the egg
especially for the embryo in later stage of development. There are two
principles strategies to ex ovo culture: whole yolk culture and explant
culture. During the whole yolk culture, the eggshell is cracked, and the contents
are transferred to a simple housing vessel. However, in explant culture
methods, the embryo is excised from the yolk and mounted in the housing vessel
to maintain membrane tension, which is important for normal development.

One of the embryonic manipulations
technique is a shell-less culture when the chick embryo is cultured in an
artificial environment without it eggshell (Kamihara et al, 2005, Kyogoku et
al, 2008). This technique very important as a way for preservation of rare
alvian species by saving the damage eggs. By using these method, it helps the
school children to observe the embryonic development in live as starting an
interesting experience for them to interest in life sciences. The hatchability
reduced as the gene introduction and other manipulation caused by windowing the
eggshell (Andacht et al,2004). This method required the fertilized eggs while
the surrogated eggshell is used as culture vessel for ex ovo culture of the
chick embryo. This cultured method included 3 system which are the embryo from
the single cell stage to the blastoderm stage is the system I then the system
II is about the embryo after the blastoderm stage until day 3 followed by for
embryo from day 3 until hatching which is in system III, in this system the
chicken eggshell was used as the culture vessel. Then embryo is transferred
from one vessel to another. Following by Naito (1990), approximately the
hatchability was improved by using this method. But some culture method that
used surrogated eggshells are reported to be quails. Kamihira (1998) reported
the quail embryo use the artificial vessel made of a gas permeable
polytetrafluoroethylene (PTFE) membrane and more quail embryos hatched by using
this method when calcium lactate was supplied. Borwornpinyo (2005), said that
the replacement of surrogate eggshells derived from different bird species
laying relatively large eggs such as aigamo duck and turkey. There are some
disadvantages of this culture method such as the preparation of eggshells,
differences among batches of eggshells, the inability of recycle use, and the
low operability during embryo manipulation. From this idea we had develop our
simple culture method with a highly hatchability by using highly convenient
transparent plastic film and we examined culture conditions such as calcium,
and water supplementation and oxygen aeration. 

The
hatching process takes about 21 to 28 days to occur after incubation under the
chicken adult’s body temperature. In this practical, the shell of the chicken
eggs will be removed, and incubation will be carried out towards the exposed
egg’s content. Calcium lactate, oxygen, benzalkonium chloride solution and
water content will be provided under the process of hatching the ‘shell-less
egg’.