Introduction | Male Anatomy |
Female Anatomy | Fertilization |
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.
- 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:
have two ovaries, each of which consists of four ovarioles. Oocytes (eggs) are produced
- Common oviduct:
- The two ovaries connect to a tube called the
- The opening through which eggs are laid is
Egg Production (Oogenesis)
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).
Continue to Fertilization