The disposition, structure and functions of the lateral line sense organs in Scoliodon:
Sense organs are structures which stand between the organism and the environment. The sense organs do not feel or sense stimuli but are simply avenues of approach to the central nervous system, which is provided with the power of sensation.
Sense organs are connected with the most peripheral part of the nervous system. Various types of receptor organs are found in the dog fish including the lateral line receptor organs or the neuromast organs, which are so characteristic of the fishes and forms a component part of the rheoreceptor organs in general.
Lateral line sense organs are situated within the lateral line canal, which may be divided into (i) a trunk and tail canal, and (ii) a head or cephalic canal.
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They are innervated by the branches of the seventh cranial nerve and the lateralis branch of the vagus. In elasmobranch fishes, the lateral line sense organs consist of a series of lateral line organs or neuromasts arranged in rows extending from one end of the body to the other.
The neuromasts lie in the dermis or deeper in the subcutaneous tissue. During development, the neuromasts sink down to form grooves, which then close over to form canals embedded in the skin but with numerous pores opening to the outside.
The lateral line canal runs from the head to the posterior end of the body along the outer edge of the horizontal septum, which divides epaxial musculature from hypaxial. The sense organs and the tubules seem to be usually metamerically arranged in the trunk and they correspond. But in the head, the metameric arrangement is not found and the sense organs are more numerous than the tubules. The walls of the canals contain stiff connective tissue to keep them open.
Each neuromast consists of a group of sensory cells accompanied by supporting cells. Each sensory cell has a hair projecting from its exposed surface.
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Lateral line sense organs probably detect vibrations in water. By means of these organs the fish is enable to face against the water flow, even in darkness or in turbid waters, when no land marks are visible, and so to maintain its position without being constantly carried downstream or away with flowing tides and currents.
These organs no doubt also help in making a fish aware of the approach of enemies which agitate the water by swimming movements, producing low vibrations that act as warning stimuli. Various stages of elaboration of the lateral line sense organs may occur at the same time in different regions of the body of a fish.