- Write a note on book lung of Buthus.
Book lungs are the aerial gas exchange structures of Buthus.
No. & location:-
Buthus possesses 4 pairs of book lungs situated on
the ventro lateral sides in the 3rd, 4th, 5th & 6th mesosomal segments.
Structure:-
Each book lungs consists of 2 parts
- Atrial chamber:-
The proximal or ventral part is called the atrial chamber. It is a
small compressed air cavity.
The roof of the atrial chamber
bears many slit like openings, set parallel with each other. The chamber
communicates with the interlamellar spaces of pulmonary chamber through these
openings.
The atrial chamber communicates with the exterior through a slit,
called stigma.
- Pulmonary chamber:-
The larger, distal or dorsal part is called the pulmonary chamber.
It contains about 150 vertical
folds or lamellae. The lamellae are lying parallel & are arranged like the
pages of a book.
Each lamella is a hollow
structure made of 2 thin layers of membrane united at their end.
The outer sides of the lamellae bear ridges & bristles which keeps
the adjacent lamellae apart & an inter-lamellar space is left between them
for the for the flow of air.
Blood supply:-
The deoxygenated blood from the ventral sinus is sent to each book lung
by a diverticulum.
Then it enters the
lamellae at their bases & is oxygenated.
The oxygenated blood from the lamellae is collected into a pulmonary
vein which opens into the pericardium.
Mechanism of
respiration:-
Dorso-ventral & atrial muscles control the inflow & outflow of
air into the atrial chamber.
On contraction of these muscles air flows out through stigmata.
On relaxation of these muscles fresh air enters into the atrial chamber
as well as interlamellar spaces.
Exchange of gases takes place through the highly vascularised walls of
the lamellae.
- Write a note on book gills of Limulus.
In xiphosuran, Limulus, the respiratory organs are book-gills.
Location:-
They occur on the posterior wall of the plate like appendages of 5
posterior segments of mesosoma.
Structure:-
They become modified as gills. On each appendage are found some 1500
thin walled lamellae formed by folding of posterior integument.
The lamellae project from the surface & since they lie parallel to
each other resembling the pages of a book, they are characteristically known as
book gills.
Mechanism of
functioning:-
The beating of the appendages causes
a current of water to pass over the book gills.
The blood within the lamellae is separated from the surrounding sea
water by only a thin wall. Blood contain respiratory pigment haemocyanin.
A major ventral blood vessel
gives rise to a series of afferent branchial vessels to supply blood to the
book gills. After the gas exchange between the water & blood efferent
vessels carry oxygenated blood to a large branchio-pericardial vessels leading
back towards the heart.
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