Ciliary muscle

“ We have, in the skeleton, a complicated apparatus of parts hinged and movable upon one another; the agent moving these parts is the same agent that we find in the heart walls propelling the blood through the circulation, in the alimentary canal squeezing the food along its course, and universally in the body where motion occurs, except in the case of the creeping phagocytes, and the ciliary waving of ciliated epithelium. This agent is muscle. We have, in muscular tissue, a very wide departure from the structure of the primordial cell ”

“ The statement has been emphasized that farsighted and astigmatic persons, up to the age of forty-five or fifty, can sometimes overcome the optical defects in their eyes by exercise of the ciliary muscle which alters the shape of the lens, and, therefore, it would be impossible for an examiner to discover the fault without putting drops in the eye, which temporarily paralyze the ciliary muscles for from thirty-six to forty-eight hours, but otherwise do no harm. ”

“ If we contemplate the movements of cilia, of a Rhizopod’s pseudopodia, of a Polype’s body, or of the long pendant tentacles of a Medusa, we shall see great congruity between them and this hypothesis. Bearing in mind that the contractile substance of developed muscle is affected not by nervous influence only, but, where nervous influence is destroyed, is made to contract by mechanical disturbance and chemical action, we may infer that it does not differ intrinsically from the primordial contractile substance which, in the lowest animals, changes its bulk under other stimuli than the nervous. ”

“ The cells of the inner layer are large, and bear cilia that protrude into the internal cavity. Their functions are those of digestion and absorption. Part of the protoplasm of the outer cells is modified into a fibrous, contractile substance, which represents the beginnings of muscle tissue. The outer layer also forms a protective skin-like covering. In the outer layer also occur a large number of stinging cells, each of which has a complex mechanism for injecting a fluid poison into any creature which should happen [44] to come in contact with them. ”

“ The body is pellucid, nearly triangular, bivalved, and open on the back of the animalculum; from the orifice proceed two little laminæ larger than the rotatory cilia; at the bottom are three or four rigid points, e f e, and a moveable tail, g, between them, divided into two filaments, which the little creature opens and shuts at pleasure; by these it fixes itself to objects. a a, the lateral cilia; b, two small laminæ; c, a deglutatory muscle; d, an opake mass.
368. Brachionus Dentatus. B. bivalvis, testa arcuata, apice et basi utrinque dentata, cauda spina duplici. ”

“ All lantern muscles are derivatives of the different epithelial sheets that constitute the lining of the peripharyngeal coelom. Like most echinoderm muscles, the lantern musculature is composed of smooth muscle fibers [4] . Previous histological and ultrastructural investigations of lantern muscles [21] , [2] , [15] , [19] , [18] , [27] , [28] , [29] have revealed that the muscles are contractile structures composed of numerous fascicles. A fascicle is composed of several muscle fibers, each of which represents a single myocyte. ”

“ A pair of excretory tubules, the {420}forerunners of the brown tubes, are found, and the chief muscle tracts are already established. The nervous system is still in close connexion with the skin, from the outer part of which it is derived; the cerebral thickening bears two eye-spots.
The fluid of the body-cavity contains corpuscles, which are kept in active circulation by the constant contractions of the body-wall, and by numerous tufts of cilia which are borne on the inner surface of the skin. The dorsal blood-vessel is one of the latest organs to arise. ”

“ The presence of collagen fibrils varies between the adaxial and the abaxial connective tissue layers. au = auricle, bl = basal lamina, cc = central cavity, cf = collagen fibril, ci = cilium, ct = connective tissue, ec = exterior cavity, ep = epithelial cell, fa = fascicle, ic = interradial cavity, ip = interpyramidal muscle, lo = lobe, mf = muscle fiber, np = nerve process, nu = nucleus, ph = pharynx, po = postural muscle, pr = protractor muscle, pv = perivisceral coelom, py = pyramid, re = retractor muscle, to = tooth. ”

“ Apart from a function connected to the presence of skeletal elements, the specific morphology of frilled protractor muscles could also provide a stabilizing function as their lobes might prevent lateral shear of the main protractor muscle element. In addition, contraction and relaxation of the lobes could lead to a more rapid exchange of the coelomic fluid located at the fluid-tissue boundary along the muscle's surface. ”

“ The surface of the male is ciliated, and the skin {439}contains circular and longitudinal muscle-fibres. The body-cavity is developed, but does not reach to either end of the body. The alimentary canal is closed, neither mouth nor anus existing; it is supported by regularly arranged dorso-ventral muscle strands. A nerve-ring and a ventral cord exist. There are also two rudimentary organs corresponding with the anal vesicles of the female, and a single nephridium which acts as a duct for the spermatozoa; the latter arise from modified cells lining the body-cavity. ”

“ The long cilia projected from the upper part form a spiral within the margin of the open mouth leading to the digestive sac. A contractile vacuole lies to the right of the oral opening. New individuals are produced by the process of budding, and in the form of ciliated embryos from the nucleus. Stentors are commonly met with in fresh water, and are usually of a brilliant green colour. These little bodies will bear cutting up: if only a fragment of the nucleus be included in the section, the injury is soon repaired. ”

“ A=orifice; B=contracted collar; C=diaphragm; D=parieto-vaginal muscles; E=tentacles; F=pharynx; G=œsophagus; H=stomach; J=intestine; K=rectum; L=intertentacular organ; M=retractor muscle; N=testes; O=ovary; P=funiculus; Q=parietal muscles; R=ectocyst; S=endocyst.
The muscular system is often of a complicated nature, but three sets of muscles may be distinguished as being of peculiar importance, viz., (i) the retractor muscles, which are fixed to the [Pg 166] base of the lophophore at one end and to the base of the zoœcium at the other, and by contracting pull the former back into the zoœcium ”

“ From the depression, two long and delicate cilia proceed, one shorter than the other, and directed forwards. Close to the origin of those cilia, in the substance of the body, is a regularly pulsating contractile vacuole. The shorter cilium vibrates actively, and effects the locomotion of the organism, while the other trails behind; the whole body rolling on its axis with its pointed end forwards. ”

“ The edge of the opening of the shoe is bordered by a fringe of cilia, the ciliary movements of 389 which keep the microscopically small and transparent nurse swimming about freely in the sea. This fringe of cilia is marked in Fig. A 2-A 4, on Plate VII., by the narrow alternately light and dark seam. The nurse then, in the first place, forms a perfectly simple intestinal canal for nutrition, mouth (o) , stomach (m) and anus (a) . Later, the windings of the fringe of cilia become more complicated, and there arise arm-like processes (Fig. A 3-D 3) . ”

“ Order I.—Section A.—Gymnostomaceae. Mouth habitually closed; swallowing an active process; cilia (or membranelles) uniform, usually distributed evenly over the body; form variable, sometimes of circular transverse section.
Section B.—Trichostomata. Mouth permanently open against the endosarc, provided with 1 or 2 undulating membranes often prolonged into an inturned pharynx; ingestion by action of oral ciliary apparatus.
Order 2.—Subsection (a) .—Aspirotrichaceae. Cilia nearly uniform, not associated with cirrhi or membranelles, nor forming a peristomial wreath. ”

“ The muscular fibres. The muscular elements of the Chordata undoubtedly belong to the myoepithelial type. The embryonic muscle-cells are at first simple epithelial cells, but soon become spindle-shaped: part of their protoplasm becomes differentiated into longitudinally placed striated muscular fibrils, while part, enclosing the nucleus, remains indifferent, and constitutes the epithelial element of the cells. The muscular fibrils are either placed at one side of the epithelial part of the cell, or in other instances (the Lamprey, the Newt, the Sturgeon, the Rabbit) surround it. ”

“ In the centre of the praeoral lobe is a tuft of cilia. Just behind the ciliated ring is a pair of larval eyes which disappear in the adult; these correspond to the cephalic eyes of Lamellibranchs. An ectodemic invagination forms a large mucous gland on the foot, which is more or less atrophied in adult life. The gonads originate by proliferation of the anterior wall of the pericardium. The shell-valves 250 arise as transverse thickenings of the dorsal cuticle behind the ciliated ring, the tegmentum being the first part formed. ”

“ The individual muscle fascicles are formed by clusters of ciliated myoepithelial cells that are lined by a basal lamina and that sink into the underlying connective tissue during ontogenesis. The loose connective tissue separates the fascicles from each other and the epithelia [16] .
Many muscle fibers are running along the whole length of the muscle, but the muscles are innervated only from the end that faces the lantern [32] . However, the innervations of the retractor, protractor, and postural muscles are independent only to some degree. ”

“ These coloured particles can readily be traced in their movements, and accordingly we see them tossed about and whirled about by the ciliary currents, and finally swept into the mouths of the animalcules, which appear always to be on the outlook, if one may so term it, for nutritive matter. Sometimes when we may be unable to see the cilia themselves, on account of the delicate structure, we may assure ourselves of their presence by noting the currents they create. ”

“ To the sternum as to the ribs is only a small part of this muscle attached.
Between the two above described muscles is found a space which is filled, in great part, with a fibrous membrane that binds the two muscles together. This membrane begins very thin and without a marked boundary behind the kidneys; it runs forward directly under them and the dorsal wall of the body, becoming gradually thicker, though never very thick, and fuses, laterad to the kidneys, with the above-mentioned aponeurosis of the two diaphragmaticus muscles. ”

“ Within the prosoma there is a strong adductor muscle, running straight from side to side, for the purpose, as it appears, of flattening the body. The thorax, on the dorsal and ventral surfaces, is well furnished with straight and oblique muscles (without striæ) , which straighten and curl up this part of the body. The muscles running into the pedicels of the cirri, cross each other on the ventral surface of the thorax; the muscles within the rami are attached to the upper segments of the pedicels. ”

“ The muscular tissue of the Hydromedusae is entirely ectodermal. The muscle-fibres arise as processes from the bases of the epithelial cells; such cells may individually become sub-epithelial in position, as in the polyp; or, in places where muscular tissue is greatly developed, as in the velum or sub-umbrella, the entire muscular epithelium may be thrown into folds in order to increase its surface, so that a deeper sub-epithelial muscular layer becomes separated completely from a more superficial body-epithelium. ”

“ The dorsal filaments are built up of columnar cells provided with long cilia, and have usually no gland cells, the others may show a few cilia but are principally composed of non-ciliated gland cells. When the bolus of food has passed through the stomodaeum it is seized by these ventral filaments and rapidly disintegrated by the secretion of its cells. The function of the dorsal mesenteric filaments is mainly respiratory. During life their cilia produce a current which flows towards the stomodaeum. ”

“ The first is, in its most primitive form, a small transparent creature, with a mouth and anus and a postoral longitudinal ciliated band (fig. 5, A) . In Asteroids the band of cilia becomes divided in such a way as to give rise to two bands, the one preoral, encircling the preoral lobe, and the other remaining postoral (fig. 5, B) . In the other groups the band remains single and longitudinal. In all cases the edges of the body carrying the ciliary bands become sinuous (fig. 6) and sometimes prolonged into arms (figs. 7-9) , and each of the four groups has its own type of larva. ”

“ If extension of a muscular colloid previously at rest, produces in it that molecular disturbance which leads to isomeric change and decrease of bulk, then there is no difficulty in explaining the movements of cilia; the formation of a contractile layer in the vascular system becomes comprehensible; each dilatation of a blood-vessel caused by a gush of blood, will be followed by a constriction; the heart will pulsate violently in proportion as it is violently distended; arteries will develop in power as the stress upon them becomes greater ”

“ These prove (Pl. 12, fig. 10) that the cells in this situation have become elongated in a longitudinal direction, and, in fact, form typical spindle-shaped embryonic muscle-cells, each with a large nucleus. Every muscle-cell extends for the whole length of a protovertebra, and in the present stage, or at any rate in stage I, acquires a peculiar granulation, which clearly foreshadows transverse striation (Pl. 12, figs. 11-13) . ”