Cilium

“ The spermatozoön is divided into three parts, the head, which is the modified nucleus of the male reproductive cell, the intermediate segment, which is the cytoplasm of the cell, and the tail, which is a veritable vibrating cilium, as found in ciliated epithelial cells. ”

“ The sensory cells are slender epithelial cells, often with a cilium or stiff protoplasmic process, and should perhaps be regarded as the only ectoderm-cells which retain the primitive ciliation of the larval ectoderm, otherwise lost in all Hydrozoa. The sense-cells form, in the first place, a diffuse system of scattered sensory cells, as in the polyp, developed chiefly on the manubrium, the tentacles and the margin of the umbrella, where they form a sensory ciliated epithelium covering the nerve-centres ”

“ Such a structure is of common occurrence among the lowest plants and animals, and is known as a contractile vacuole.
The little creature thus described sometimes propelled itself with great activity, with a curious rolling motion, by the lashing of the front cilium, while the second cilium trailed behind; sometimes it anchored itself by the hinder cilium and was spun round by the working of the other, its motions resembling those of an anchor buoy in a heavy sea. Sometimes, when two were in full career towards one another, each would appear dexterously to get out of the other's way ”

“ From the large size of each cilium they are very favorable creatures for exhibiting the real nature of the action, which gives rise to the rotatory appearance, and which can be easier studied than described. ”

“ The cilium or flagellum may often be traced a certain distance into the substance of the cytoplasm to end in a dot of denser, {19}readily-staining plasm, which corresponds to a "centrosome" or centre of plasmic forces (see below, pp. 115, 121, 141) ; it has been termed a "blepharoplast." [26]
Again, the cytoplasm may have differentiated in it definite streaks of specially contractile character; such streaks within its substance are called "myonemes"; they are, in fact, muscular fibrils. ”

“ From my inability to demonstrate sensory cells in the nerves of Charybdea, I by no means wish to deny their existence; for that remains to be proved, or disproved, by macerations. At any rate, [41] they cannot be so numerous as has been supposed. The position of the nuclei shows that.
The epithelium of the nerve is said by Claus to be ciliated. It has been suggested by Schewiakoff that probably in such cases the sensory cells bear one long cilium, while the supporting cells have many smaller cilia. ”

“ Mouth in the anterior third of the body. The left edge of the mouth carries a distinct undulating membrane; the right edge is plain, longitudinally striated and bears cilia. It is slightly depressed and the depression is carried posteriorly in the form of a shallow furrow which reaches to the posterior end. The contractile vacuole is on the left side, the spheroidal nucleus on the right side of the furrow. The body is uniformly covered with fine cilia, and the periphery is uniformly studded with large trichocysts, except along the furrow. Food consists of dinoflagellates and other small forms. ”

“ 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 embryo early becomes a "blastosphere" or hollow vesicle formed of a single layer of cells. One half of this is invaginated, or pushed into the other half, and a "gastrula" is thus developed, the cavity of which is the "archenteron," and the two cell-layers respectively "ectoderm" and "endoderm." The "blastopore," or orifice of invagination, is at the posterior pole of the larva, where it narrows and closes, the locomotor, transverse band of cilia developing round it. No other bands of cilia appear in this form of development. ”

“ 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. ”

“ Ciliary action was at first vigorous in both, perhaps more so in that subjected to the poisoned solution. Eight minutes later, non-poisoned cilia still active, poisoned cilia very feeble. Ten minutes, non-poisoned cilia still active, poisoned very feeble. Fourteen minutes, non-poisoned cilia still active, poisoned cilia very languid. Twenty minutes, non-poisoned cilia still active, poisoned cilia perfectly inactive. From this it is evident that the poison first stimulates and then destroys the activity of the cilia. The action of the poison on vegetable protoplasm is very different. ”

“ These cilia appear to be attached to the cell-wall, being unaffected by plasmolysis, but Fischer states that they really are derived from the central protoplasm and pass through minute pores in the wall. The cilia may be present during a short period only in the life of a Schizomycete, and their number may vary according to the medium on which the organism is growing. Nevertheless, there is more or less constancy in the type of distribution, &c., of the cilia for each species when growing at its best. ”

“ The protoplasm of Ciliata is the most differentiated that we {141}find in the Protista, and we can speak without exaggeration of the "organs" formed thereby.
The form of the body, determined by the firm pellicle or plasmic membrane, is fairly constant for each species, though it may be subject to temporary flexures and contractions. The pellicle varies in rigidity; where the cilia are abundant it is proportionately delicate, and scarcely differs from the ectoplasm proper, save for not being alveolate. In the Peritrichaceae it is especially resistant and proof against decay. ”

“ The rotating organs from which these fascinating animalcula derive their name consist of two disc-like bodies whose margins are fringed with rows of cilia, which create currents toward the oral aperture, and which have given rise to the optical delusion of rotating wheels. The disposition of the cilia is so arranged as to bring food to the rotifer and conduct it to the mastax or digesting apparatus—a muscular bulb moved by a series of muscles—the gastric glands and stomach. The great transparency of the whole structure permits of the animal economy being easily studied. ”

“ The pharynx (p) is long, and contains an undulating membrane (u.m) on its inner side projecting out through the mouth, and numerous cilia; it leads deep into the body (p) . The first part is distinguished as the "vestibule" (v) , as into it opens the anus, and the contractile vacuole (c.v.) , the latter sometimes opening by a reservoir (r) . The body contains in the ectoplasm {157}myonema-fibrils which, by their contraction, withdraw the disc, and at the same time circular fibrils close the peristome over it. ”

“ This wandering half or head is now seen to be provided at each end with cilia, and by means of these filaments swims freely throughout the surrounding water. After a time, however, it settles down, develops a stalk from what was originally its mouth extremity; whilst the opposite or lower extremity with its fringe of cilia comes to represent the mouth of the new animalcule. We thus note that new bell-animalcules may be produced by the division of the original body into two halves. They also increase by a process of budding. New buds grow out from the body near the attachment of the stalk ”

“ It at first forms a ciliated tube on each side, placed in front of that part of the larva which becomes the trunk of the adult. It opens to the exterior by a fine pore on the ventral side, immediately in front of one of the mesoblastic bands, and appears to be formed of perforated cells. It terminates internally in a slight swelling, which represents the normal internal ciliated funnel. The primitively simple excretory organ becomes eventually highly complex by the formation of numerous branches, each ending in a slightly swollen extremity. ”

“ The Infusoria, a name originally of much wider application, is now restricted to denote those Protozoa in which locomotion or capture of food is effected by means of special organs termed cilia, minute hair-like contractile extensions of the protoplasm differing from flagella not only in their usually smaller size and greater number, but also in the mode of contraction and movement. The cilia may be present throughout life or only in an early stage of the individual. ”

“ The ectoplasm is less refractile than the rest of the cytoplasm; it also stains less intensely (fig. 1) , and is best seen on protrusion of a pseudopodium. Red blood corpuscles are rarely, if ever, found ingested in the cytoplasm.
Fig. 3.—Entamœba coli: life-cycle, a-e, stages in binary fission; A-D, schizogony, with formation of eight merozoites; 2–10, cyst formation or sporogony, with formation of eight nucleate cysts. (After Castellani and Chalmers)
The nucleus is vesicular, and is spherical when inactive, measuring 5 μ to 7 μ, with a thick nuclear membrane. ”

“ 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) . ”

“ We now define it thus:—Protozoa bounded by a permanent plasmic pellicle and consequently of definite form, never using pseudopodia for locomotion or ingestion, provided (at least in the young state) with numerous cilia or organs derived from cilia and equipped with a double nuclear apparatus: the larger (mega-) nucleus usually dividing by constriction, and disappearing during conjugation: the smaller (micro-) nucleus (sometimes multiple) dividing by mitosis, and entering into conjugation and giving rise to the cycle of nuclei both large and small of the race succeeding conjugation. ”

“ 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. ”

“ They have cilia externally, and a cutis which secretes similar hyaline tubes to those of many Annelida. The muscular system ia greatly developed, and iu definite layers, and many swini as freely as the most active leeches. The digestive system intimately agrees, having cilia on the inner surface of the canal, a muscular cesophageal region, and a sacculated intestine, while the glandular and other elements in the wall are very similar; it differs in not passing through a buccal nervous collar, although it lies beneath the nervous system in this region. ”

“ We have seen that the cilia create miniature maëlstroms or whirlpools in the surrounding water, which have the effect of drawing particles of food towards the mouth. The study of the bell-animalcules affords an excellent example of the gaps which yet remain to be filled up in our knowledge of the structure even of the lowest and commonest forms of life. No structures are more frequently met with in the animal world than the delicate vibratile filaments or cilia, so well seen in the bell-animalcules. The microscopist meets with them in almost every group of animals he can examine. ”

“ The anus (cytopyge) is terminal. The macronucleus is usually horse-shoe or kidney-shaped, sometimes oval; the micronucleus contiguous. Reproduction is by binary fission and conjugation, and encystment occurs. The cysts are spherical or oval. These ciliates are parasitic in the large intestine of human beings and pigs, in Amphibia, and in the body cavity of polychæte Annelida.
Fig. 113.—Balantidium coli. a, nucleus; b, vacuole; c, peristome; d, bolus of food. (After Leuckart.) ”

“ In one group of infusoria (Hypotricha) , the cilia, “cirri,” have attained a high degree of differentiation, and reach a considerable size. Both cilia and flagella spring directly from the cell-protoplasm, piercing the cell-membrane, when this is present. At the point where they become continuous with the cell-body there is usually a deeply staining “basal granule.” In some cases the flagella are in direct connexion with the centrosome (see below, Cell-division) , e.g. ”