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Female Reproductive Tract |
Egg Production
Female Reproductive Tract
- Bursa copulatrix:
- The bursa copulatrix is a sac-like organ in female
Lepidoptera in which the spermatophore is stored immediately after
mating. It secretes enzymes that break the spermatophore down
into nutrients that can be used by the female.
- Sperm duct:
- The ductus seminalis, or sperm duct, is a tube
that connects the bursa copulatrix to the common oviduct. Sperm
move through it to get to the spermatheca.
- Spermatheca:
- Sperm are stored in the spermatheca , a storage
pouch at the end of a long, tubular gland called the spermathecal
gland. This gland produces secretions that probably provide nutrients
for the sperm.
- Ovaries and Ovarioles:
- Lepidoptera have two ovaries, each of which consists
of four ovarioles. Oocytes (eggs) are produced here.
- Common oviduct:
- The two ovaries connect to a tube called the common
oviduct.
- Vulva:
- The opening through which eggs are laid is the
vulva.
The end of the ovariole is called the germarium,
where oocytes are produced from the original germ cells. This process
begins during the larval stage, and continues in the adult. After
the female monarch ecloses, the oocytes begin to move down the ovariole,
enlarging as they go through the vitellarium, where
yolk is deposited on them. This process is called vitellogenesis.
The yolk contains both protein and lipids. In some Lepidoptera,
vitellogenesis occurs before the adult stage; in these species females
eclose with their eggs fully developed and can mate and lay eggs
soon afterwards. Vitellogenesis doesn’t begin in monarchs until
the adult stage.
The last stage of oogenesis is the formation of the
egg-shell, or chorion. The chorion is a protective
layer produced by cells in the ovarioles. It contains small, water-repellent
pores through which air is exchanged, and small openings called
micropyles through which the sperm will enter the egg to fertilize
it. The monarch chorion is covered with vertical ridges. Oogenesis
continues throughout female monarchs’ lives, so their ovarioles
usually contain a series of oocytes in successive stages of development.
We have done several research projects in which we
studied when egg development occurs in monarchs, and how long it
takes (if you wish, skip ahead to Research
Questions on Monarch Reproduction).
on to Fertilization
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