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| An in depth analysis of Scorpion Digestive system |
By:
Snigdha |
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A. Alimentary Canal
The alimentary canal is a fairly uniform and straight tube from mouth to anus. It may be divided into four regions: (I) pre-oral cavity, (2) fore-gut, (3) mid-gut, and (4) hind-gut.
A large open, pre-oral cavity is formed in front of the mouth by the coxae of the first four pairs of the prosomatic appendages. Dorsally, it is bounded by the two chelicerae and the median rostrum or labrum. Laterally, it is guarded by the coxae of the pedipaips. Yentrally, the floor is formed by the two pairs of maxillary processes the first two pairs of legs.
2. Fore-gut or stomodaeum
Fore-gut includes the rnouth, the pharynx and the oesophagus, and is internally lined- by cuticle. The mouth is a small, narrow and oransverse aperture situated, behind the gutter- like pre-oral cavity, below the base of the labrum and leads into the pharynx. The narrow mouth can only admit juices and puips.
The pharynx is a large, pear-shaped, muscular and suctorial chamber with elastic walls capable of great dilatation, due to many radiating bundles of muscles running outward from it to the wall of the cephalothorax. These muscles enable the pharynx to work as a sucking organ, so that the liquid-food is sucked through the mouth. The pharynx is followed by a small narrow tube, the oesophagus, which passes through the cephalic nerve ring. It extends into the stomach to form a sleeve-valve which prevents regurgitation of food.
It includes stomach, intestine and two digestive glands and is internally lined by epitbelium. The aesophagus leads into a short and dilated stomach extending up to the diaphragm. A trilobed, brownish gland, lying in the cephalothorax, opens into the stomach. Huxley regarded it to be salivary gland; but Blanchard and Pavlovsky did not accept this view and called it stomach gland.
The intestine is the longest part of the alimentary canal, running up to the last segment of the abdomen, where it passes into the hind-gut. It is a wide tube with glandular walls and differentiated into two distinct regions, the preabdominal portion or pars-tecta-intestini, and the post-abdominal portion or pars-nuda-intestini. The junction of these two regions is marked by a narrow constriction, from where arise one or two pairs of narrow, elongated and blind tubes, the Malpighian tubules, which are excretory in function.
A large, brownish and lobulated glandular mass, called the liver or hepatopancreas, occupies nearly the whole of the pre-abdominal cavity. The heart lies in a mid-dorsal longitudinal groove of the hepatopancreas, while the intestine and other internal organs are found embedded in it. Five pairs of lateral, narrow, hepatic ducts lead from the hepatopancreas to open into the intestine. The hepatopancreas is a racemose gland consisting of a mass of small tubules, which are in communication with the hepatic ducts in the same way as the twigs of a tree are with the main stem. The hepatic function of liver is doubtful, but due to its large bulk it seems to perform other important functions besides secreting digestive juices. It is t h e smallest part of the alimentary canal restricted only within the last metasomatic segment. It is internally lined by chitin and opens to the exterior through the anal aperture situtated ventrally at the base of telson.
B. Food and Feeding Mechanism
The scorpions are carnivorous and predaceous and they feed upon small animals like insects, spiders, etc. They can remain alive without food for nearly six months. They are also cannibals and often feed upon other smaller scorpions. The mouth of scorpion is very small, so it cannot feed on solid particles; but it only sucks the liquids from the body of the prey.
The prey is seized by the chelate pedipalps and trans-. ferred to the pre-oral cavity and torn to pieces by the chelicerae. If the victim is large and struggling too violently, the poison-sting is, rapidly jerked forwards and the victim is quickly paralysed. The basal segments of the appendages forming the pre-oral cavity are slowly pressed upon the prey, which is gradually squeezed and the oozing liquids are sucked in by the muscular pharynx. The process. of feeding is very slow requiring at least two hours to devour a cockroach.
C. Digestion
Inside the pre-oral cavity the food is reduced to pulp and its proteins partially digested by the secretion of certain alveolar glands, found in the maxillary processes of the first two pairs of legs. Inside the stomach this partially digested food is mixed with the secretion of the stomach gland containing the enzymes, amylase, trypsin, lipase, etc. The digested food is absorbed into the intestine, while the undigested portion reaches the hind-gut to be expelled through the anus. |
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