isa-normaladvance-1909-00106

Description:	106THE NORMAL ADVANCEMussels are slow moving creatures and theymust wait for their food to come to them ratherthan seek it. Their food consists of very smallorganisms but chiefly plants. At the posteriorend of the animals body there are two openings, the siphons. These siphons are formedby the folds of the mantle which line the shell.A current of water with its contained organisms is constantly being drawn in at the lowersiphon- This water bathes the gills, purifiesthe blood, and at the same time many of thefood particles are caught and conveyed to themouth. The water is finally thrown out at theupper or exhalent siphon. The current ofwater just described is produced by the vibration of numerous fine cilia which cover thegills and other parts of the interior of thebody.It has been stated that mussels are slow moving, which is true, when they are comparedwith other animals, but some observationsmade during the past summer show that amussel may travel farther during a night thanmany have supposed. Stakes with labels wereplaced by a number of mussels at four oclockin the evening and at nine oclock the nextmorning the distance which each had traveledwas measured. It was found that some hadgone as far as 11 feet. One individual timedfrom nine in the morning until three in theafternoon traveled twenty feet and six inches.This latter mussel was in shallow water whichwas rapidly falling.When the water is fairly quiet it is veryeasy to follow the track of a mussel in the sandor mud. The mussel has a large flat portion,muscular in structure, which is known as thefoot. The foot can be pushed out anteriorlyfrom between the valves of the shell and downinto the mud or sand When the foot hasbeen forced down to a considerable depth theanimal then pulls its shell and the remainderof the body forward. Mussels which arestranded on sand bars and exposed flats maywander about and finally reach water againbut there is no evidence to show that theseanimals have any way to tell in which directionto go. If they do find water it is by merechance. The majority of those that are uncovered for any length of time perish.The fresh water mussel has no eyes but itis very sensitive to variations in light. Eventhe shadow of a lead pencil cast on the siphonsof an animal may cause the siphons to immedi-tely withdraw. Mussels evidently have somesense of taste and they may smell but there isno experimental proof of either.The shell of the mussel consists of Wo halveswTith an outer covering of animal matter, amiddle prismatic layer and an inner, thickerlayer of mother of pearl. The latter layer isthe portion from which buttons are made. Theshell grows larger at the edges and thicker asthe mussel ages, layer after layer of the motherof pearl being deposited on the inside of theshell. Mussels never shed their shells so theolder the animal the thicker the shell, unlessthe water contains some solvent which gradually dissolves the shell from the outside.Mussels reproduce by means of eggs, butthe eggs are not cast out of the mother tohatch and shift for themselves at once. Theyare caught in the membranes of the outer gillswhere they develop for several weeks into theyoung, which are not very much like the adultmussel. At this stage the young mussel isknown as a glochidium. It possesses two hooksand a sucker-like tube, the byssus. Whenthe glochidium is mature it escapes from themother but it is not yet able to live an independent existence so it must clasp to the finsor other portion of some fish, tadpole, or someother suitable water animal. The glochidiumsoon buries itself in the skin of its host andhere lives a parasitic life for four to eightweeks, at which time it is shed from its host,falls to the bottom of the stream or lake and,if the conditions are favorable, it may developinto an adult mussel. The chances are thatthe great majority of the glochidia will neverfind a host, consequently they must perish assoon as they are discharged from the parent.Should the glochidia find a host they may notdevelop, and if they do, there is a possibility
Source:	http://indstate.contentdm.oclc.org/cdm/ref/collection/isuarchive/id/34136
Collection:	Indiana State University Archives

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