Page:The New International Encyclopædia 1st ed. v. 14.djvu/187

MUSCI. 151 MUSCLE AND MUSCULAR TISSUE. body ( protonenia ) , U])on which appear buds that give ri^o to the (iidinaiy leafy iiidss ])lant. Upon this h'afy phint the sex organs (antheridia and archegonia) are borne ( Fig. 1 ) , an<l lience it is the sexual phase (gametoph_i-te| in llie alternating generations. The sex organs produce a fertilized egg. which upon germination does not reproduce a leafy moss plant, but a structure of totally dif- ferent character, namely a .stalked spore-case (sporogonium) , full of asexual spores, commonly called the moss 'fruit.' Since this sporogonium has no sex organs, it is the se.xless phase (sporo- phyte) in the alternation. When these spores germinate they produce leafy moss plants (ganie- tophytes) again, and so alternation continues. (See Fig. 2.) The spore-case (capsule) of an or- dinary moss, generally pendent from a slender stalk (seta) , is a very complicated structure. It is usually somewhat urn-shaped, with a little coni- cal or flatfish lid (operculum), which is thrown off when the spores are to be discharged. Often quite common in the Tertiary rocks and esi)ccial- ly so in the amber. MUS'CID.a; (Xeo-Lat. nom. pi., from Lat. muscii, tly). A family of dipterous insects com- prising the typical or true Hies. The bristle of the antenn.ne is feathery and the abdomen is smooth except for a certain number of bristles near the tip. The larva? as a rule feed upon de- caying animal or vegetable matter, more abun- dantly upon the former. The group comprises naany species, and includes some of the most common and abundant forms, such as the house- fly, the horn-fly, and the stable-fly (qq.v. ). MUSCLE AND MUSCULAR TISSUE. While contractility is a. property of all active, living protoplasm, it is in nuiscular tissue that this property reaches its highest development, the abilitj' to contract along certain definite lines being the peculiar function of this tissue. Muscle Fig. 3. 1, the younj? aporoph.yte ir) rupturing the bladder.v archegoiiium aud carr.viufj; up the upper portion (r) as a Iiood (calyptra). 2, mature sporophyte (sporo- gonium), showing foot (fi.sota (.r), capsule (f), and oper- culum (o). Both diagrammatic. also the moutli of the urn is guarded by Iieautiful hair-like or tooth-like structures which con- verge toward the centre, and are coUettively known as the ^)eristouie (around the mouth). Through the centre of the ca])sule there runs an axis of sterile tissue, called the columella; while capping the top of the capsule like a loose hood is the calyptra, which is the dead and ruptured female sex organ (archegonium) that has been carried up by the elongating sporogonium (Fig. 3 ) . See Beyopiiytes. Fossil ilossES. The earliest fossil mosses, ^luscites, allied to the modern genus Polytri- chum, are found in the Carboniferous rocks of Conimentry, France. Throughout the Mesozoic formations fossil mosses are rare, though their existence during the Liassic is inferred from the presence in rocks of that age of a beetle of the genus Birrhus, which at the present time is known to live in mosses onlv. Fossil mosses are A. BICEPS MC8CLE. tissue occurs in three different forms : ( 1 ) Striated Voluntary Muscle. This form of muscle is found in all those muscles which are under the control of the will, in fact all those which in the common use of the term are called 'muscles/ ISVOLUSTAttV MUSCLE IN LONGITUDINAL SECTION. such, e.g. as the biceps, triceps, etc. (2) Xon^ striated Invohintartj Muscle. This form of muscle occurs in the muscles which are not under the control of the will, those which carry on the auto- matic functions of life, such as the muscles of the intestine, which con- trol its peristaltic action, or the muscles of the arteries and veins, which govern their contractil- ity. (.3) .S'fWaffd Tnvot- iintary Muscle or Cardiac Muscle. This is a pecu- liar form of muscular tissue found only in the heart. It appears to occupy a sort of interme- diate position between the other two forms. (1) Xoii-striated Involuntary Muscle. This form of muscular tissue, while not occurring in any .such large masses as does the voluntary muscle, has an extremely wide distribution. It forms the muscularis niucosa> and muscular coats of the gastrointestinal canal, the muscular walls Iir'OLDNTARY MUSCLE IN TRA^'SVERSE SECTION. Ar.t.. areolar tissue.