7. STRUCTURAL
ORGANISATION IN ANIMALS
ANATOMY OF COCKROACH
· Foregut:
It is lined by cuticle. It includes
Mouth → pharynx →
oesophagus → crop (to store food) → gizzard
(proventriculus).
Gizzard
helps in grinding the food. It has an outer layer of thick circular muscles and
thick inner cuticle forming 6 chitinous plates (teeth).
·
Mid
gut (Mesenteron): It is not lined by
cuticle. 6-8 tubules (hepatic or gastric caecae) are seen at the junction of foregut & mid gut. They secrete
digestive juice.
At the junction of mid gut & hindgut,
there are 100-150 yellow coloured
thin filamentous Malpighian tubules.
· Hindgut:
It is broader than mid gut and lined internally by cuticle. Hindgut includes ileum, colon & rectum. Rectum opens out
through anus.
Circulatory system
- Blood
vascular system: open type.
- Blood
vessels are poorly developed and open into space (haemocoel).
-
- Haemolymph= colourless
plasma + haemocytes.
- Heart
consists of elongated muscular tube lying along mid dorsal line of thorax and
abdomen.
- It
has funnel-shaped chambers with ostia
on either side.
- Blood
from sinuses enter heart through ostia and is pumped anteriorly to sinuses
again.
Respiratory system
- It
consists of a network of trachea
that open through 10 pairs of small
holes called spiracles present on
the lateral side of the body.
- The
thin branches of tracheal tubes are
called tracheoles. They carry oxygen
from the air to all parts.
- The
opening of the spiracles is regulated by sphincters.
- Gas
exchange takes place at the tracheoles by diffusion.
Excretory system
- Uricotelic.
Excretory organ is Malpighian tubules.
- Each
tubule is lined by glandular and ciliated cells. They absorb nitrogenous wastes
and convert them into uric acid which
is excreted out through the hindgut.
- Fat body, nephrocytes
& urecose glands also help in excretion.
Nervous system
- It
consists of segmentally arranged ganglia
joined by paired longitudinal connectives on the ventral side.
- 3
ganglia lie in the thorax and 6 in the abdomen.
- The
head holds only a bit of nervous system. Remaining part is situated along the
ventral part of the body. So, if the head of cockroach is cut off, it will
still live for one week.
- The
supra-oesophageal ganglion (brain)
supplies nerves to antennae and compound eyes.
- Sense
organs: Antennae,
eyes, maxillary palps, labial palps, anal cerci etc.
-
Sensory receptors of antennae
monitor the environment.
- Each
compound eye consists of about 2000
hexagonal ommatidia. Using these, a cockroach can receive several images of
an object. This is called mosaic vision.
It has more sensitivity but less resolution, being common during night
(hence called nocturnal vision).
Reproductive system
Cockroaches are dioecious.
Male reproductive system:
It
consists of a pair of testes, seminal
vesicles, accessory glands & external genitalia.
§ Testes: Lie
laterally in the 4th -6th
abdominal segments.
Each testis
→ a thin vas deferens → seminal vesicle → ejaculatory duct → male
gonopore.
§ Seminal vesicles:
To store sperms. Sperms are glued together to form bundles called spermatophores. They are discharged during copulation.
§ Accessory glands: Include
a mushroom gland (in 6th-7th abdominal
segments) and phallic gland.
Their secretions nourish the sperms.
§ External genitalia (male gonapophysis or phallomeres): Chitinous asymmetrical structures, surrounding the male gonopore.
Female reproductive system:
§ It
consists of 2 large ovaries, oviducts, spermatheca, genital
chamber, Colleterial glands etc.
§ Ovaries lie
laterally in the 2nd – 6th
abdominal segments. Each ovary is formed of 8 ovarian tubules
(ovarioles), containing a chain of developing ova.
§ Oviducts of
each ovary unite into a single median
oviduct (vagina) which opens into the genital
chamber.
§ A
pair of spermatheca is present in
the 6th segment which
opens into the genital chamber.
§ Sperms
are transferred through spermatophores. Their fertilised eggs are encased in oothecae.
§ Ootheca
is dark reddish to blackish brown capsule, 8 mm long. Females lay 9-10 oothecae, each
contain 14-16 eggs.
- Development
of P. americana is paurometabolous, (development through nymphal stage).
- Nymphs
look like adults. They moult 13 times
to reach the
adult form. The next to last nymphal stage
has wing pads. Only adult
cockroaches have wings.
ECONOMIC IMPORTANCE OF COCKROACH
They are pests because they destroy food and contaminate it with their smelly excreta. They also transmit bacterial diseases like cholera, typhoid, tuberculosis etc.
