Spikelet

“ Female spikelets are collected in large globose heads of stellately spreading very long rigid rod-like processes surrounded by shorter subulate bracts. Each spikelet is solitary, and articulate at the very base of a rachis, lanceolate, 1-flowered. There are four glumes. The first three glumes are as in the male spikelets, but larger. The third is paleate, empty. The fourth glume has a female flower. The lodicules are large and nerved. Styles are long, free, with short, feathery stigmas. Grain free within the hardened glumes. ”

“ Spikelets 1-flowered, crowded in a dense spike or spike-like panicle. Lower glumes persistent, membranaceous, acute, ciliate-carinate, awnless; flowering glume similar, a little longer, and a little exceeding the palet. Stamens 3.—Low cespitose annuals; spike often scarcely exserted from the upper sheath. (Name from ἕλος, a meadow, and χλόα, grass.)
H. schœnoìdes, Host. Usually nearly prostrate and tufted; leaves rather rigid, tapering to a sharp point; spike oblong, thick, 7–20 ́ ́ long. ”

“ Leaf-sheaths covered with soft hairs. 6. A. Wightianus Pedicels of upper spikelets not half as long as the sessile spikelet. Leaves glabrous and narrow 7. A. monticola. AA. The lowest one or more sessile spikelets in all racemes, or at least in one or two, differing from all those above. Racemes digitate, rarely solitary, spikelets all alike in form but differing in sex. Pedicel 1/3 as long as the sessile spikelets; nodes usually glabrous; ligule usually short and membranous. 8. A. caricosus. Pedicel 1/2 as long as the sessile spikelets; nodes bearded; ligule large and membranous. ”

“ Spikelets ovate or lance-ovate, laterally compressed, several- (2–10-) flowered, in an open panicle. Empty glumes mostly shorter than the flowers, the lower smaller; flowering glume membranaceo-herbaceous, with a delicate scarious margin, compressed-keeled, pointless, 5-nerved (the intermediate nerves more obscure or obsolete) , the principal nerves commonly clothed with soft hairs at and toward the often cobwebby base; palet membranaceous, 2-toothed. Stamens 2 or 3. Stigmas simply plumose. Grain oblong, free.—Culms tufted, from perennial roots, except n. ”

“ A spike bearing female flowers only, and covered with scales, is a strobilus, as in the hop. In grasses there are usually numerous sessile flowers arranged in small spikes, called locustae or spikelets, which are either set closely along a central axis, or produced on secondary axes formed by the branching of the central one ”

“ Inflorescence consisting of spikelets, rarely of single flowers, usually enclosed by 2 glumes (outer or empty glumes) and arranged in spikes, racemes, or panicles. Flowers in the axil of the flowering glume (or valve) , subtended by the usually 2-keeled palea and sometimes by one or two, rarely more, minute lodicules. Perianth none. Stamens 1-6, usually 3. Anthers opening by 2 slits or pores. Ovary 1-celled. Ovule 1, erect or laterally affixed, slightly curved, with the micropyle turned downwards. Styles 2, rarely 3 or 1. Fruit indehiscent; pericarp usually dry and adnate to the seed. ”

“ Dermal Bones of Reptiles. Tilgate Forest.
The structure of these bodies is very remarkable; upon closely inspecting the under side, and the surface exposed by a transverse fracture, very minute osseous spicula, decussating each other at right angles, are distinctly seen; as shown in Lign. 208, fig. 1a. In fig. 1b, a thin slice of the same, highly magnified, and viewed by transmitted light, displays medullary canals, with very fine lines radiating from them. The peculiar character of this organization consists in the disposition of the straight bony spicula ”

“ Skeleton-spicules smooth, sharply pointed, nearly straight, moderately slender, about twenty times as long as their greatest transverse diameter. Flesh-spicules occasionally amphioxous or birotulate and with a single shaft, more frequently consisting of many shafts meeting in a distinct central nodule, which is itself smooth; the shafts irregularly spiny, usually more or less nodular at the tip, which often bears a distinct circle of recurved spines that give it a rotulate appearance. ”

“ Fig. 328—A piece of the axial rod (chorda dorsalis) , from a sheep embryo. a cuticular sheath, b cells. (From Kölliker.)
In order to get a clear idea of the chief features of the development of the human skeleton, we must first examine its composition in the adult frame (Fig. 325, the human skeleton seen from the right; Fig. 326, front view of the whole skeleton) . As in other mammals, we distinguish first between the axial or dorsal skeleton and the skeleton of the limbs. The axial skeleton consists of the vertebral column (the skeleton of the trunk) and the skull (skeleton of the head) ”

“ What is the teaching of the vertebrate? What evidence is there as to the origin of the bony skeleton in the vertebrate phylum itself?
The axial bony skeleton of the higher Mammalia consists of two parts, (1) the vertebral column with its attached bony parts, and (2) the cranio-facial skeleton. Of these two parts, the bony tissue of the first arises in the embryo from cartilage, of the second partly from cartilage, partly from membrane. ”

“ The surface is compact and smooth, of a delicate purplish-grey hue, with a few minute orifices, each surrounded by a small paler area.
The spicula in this noble species are various: simple rods, straight, thick, long, slightly spindle-shaped, blunt at both ends, with a linear axis; three-rayed, large, stout, very unequal angled, without any central channel; a number of very small five- and six-rayed stars, the rays projecting in different planes. They are set in a dense, yellow, gelatinous flesh, in which we may at all times discover many gemmules, or eggs ”

“ Bone Formation.—Most of the skull and face bones begin as membranes of connective tissue, that is, are formed in membrane. Bones are also formed in cartilage, the bone formation in this case beginning from centers of ossification, where the deposit of lime salts in the intercellular substance begins, the salts coming to the centers dissolved in the plasma. Such a center of growth in a bone is called the epiphysis and is separated from the main part of the bone or diaphysis by cartilage until full growth is attained, when ossification becomes complete. ”

“ Rhaphidozoum polymorphum, n. sp.
Spicula of three different kinds; simple needles, radiate, and geminate mixed. The simple needles straight and stout. The radiate spicula commonly with three or six, rarely four or five, rays. The geminate-radiate spicula prevalent, with three or four, rarely two or five, shanks on each end of the middle rod. Number very variable. All shanks straight and smooth.
Dimensions.—Diameter of the capsule 0.1 to 0.2, length of the spicula 0.05 to 0.15. ”

“ Black and shining; the face, mandibles, head beneath, legs, pectus, sides of the thorax beneath the wings, the scutellum and the basal half of the abdomen beneath, pale ferruginous; the mesothorax with two longitudinal oblique lines on the disk, which have two parallel ones between them; the metathorax coarsely rugose; the wings dark brown, with the base of the stigma pale, and a hyaline spot beneath it. Abdomen very smooth and shining, with the apical margins of the segments narrowly rufo-piceous; the posterior legs incrassate and dark rufo-piceous. ”

“ As each bone was furnished with at least two fasciculi of fibres, one for contraction, the other for expansion, we have a hundred and fifty thousand bones, and three hundred thousand fasciculi of fibres equivalent to muscles, in the body of a single Pentacrinite—an amount of muscular apparatus concerned in regulating the ossicula of the skeleton, infinitely exceeding any that has been yet observed throughout the entire animal creation. ”

“ The only character sufficient for the constitution of genera in this transformistic group is found in the form and composition of the spicula; the very variable form of the jelly-calymma and the enclosed central capsule being without value for this purpose. But also the form of the spicula is very variable, and not always constant. In some species the particular form of the spicula is transmitted by constant heredity, whilst in others it is very inconstant, even in one and the same individual. ”

“ But in the case of the true Placoids that analogy is faint indeed. Their skeletons contain true bone;—the vertebral joints of the Sharks and Rays possess each, as has been shown, an osseous nucleus, which retains, when subjected to the heat of a common fire, the complete form of the joint; and their cranial framework has its surface always covered over with hard osseous points. But though their skeletons possess thus their modicum of bone, unlike those of embryonic birds or mammals, they contain, in what is properly their cartilage, no gelatine. ”

“ The scales of the back are small and unequal; they gradually increase in size as they approach the base of the conical spines, which is surrounded with a ring of larger scales with longer spines; the large spines are conical; rather compressed, spinulose below, smooth and acute at the tip, and are usually furnished with a sharp-toothed ridge on the front edge, and sometimes on both. These spines only consist of a horny sheath, placed on a fleshy process of the exact form and appearance of the spines they bear. ”

“ Spicula of two different kinds; one kind simple, needle-shaped, curved, thin; the other kind geminate, with a variable number of shanks on both ends of the shorter middle rod, often different on the two poles of it. The prevalent number of rays on each end is three or four, often also two or five, rarely six. All spicula smooth, more or less bent. ”

“ In the remarkable genus Monorhaphis we find a single gigantic diact spicule, which may attain a length of two or three feet and the thickness of a lead pencil, transfixing the body of the sponge like a skewer from above downwards. A special dermal skeleton is usually formed by a number of spicules distinguished as dermalia, and a gastral skeleton may be similarly formed by special gastralia surrounding the central gastral cavity. ”

“ The skeleton is cartilaginous, the skull without sutures, and the notochord more or less fully replaced or inclosed by vertebral segments. The jaws are peculiar in structure, as are also the teeth, which are usually highly specialized and found on the jaws only. There are no membrane bones; the shoulder-girdle is well developed, each half of one piece of cartilage, and the ventral fins, with the pelvic-girdle, are always present, always many-rayed, and abdominal in position. The skin is covered with placoid scales, or shagreen, or with bony bucklers, or else it is naked. ”

“ Let us now imagine a spicule, whose natural tendency is to grow into a straight linear element, either by reason of its own molecular anisotropy, or because it is deposited about a thread-like axis; and let us suppose that it is confined either within a cell-wall or in adhesion thereto; it at once follows that its line of growth will be simply a geodetic to the surface of the cell. And if the cell be an imperfect sphere, or a more or less regular ellipsoid, the spicule will tend to grow into one or other of three forms: either a plane curve of circular arc ”

“ In the adult it may, in the more primitive forms (Cyclostomata, Dipneusti) , persist as an important part of the skeleton, but as a rule it merely forms the foundation on which the cartilaginous or bony vertebral column is laid down.
2. Cartilaginous or Chondral Skeleton.— (A) Vertebral column. [27] In the embryonic connective tissue or mesenchyme lying just outside the primary sheath of the notochord there are developed a dorsal and a ventral series of paired nodules of cartilage known as arcualia (fig. 13, d.a, v.a) . ”

“ The position appears to me to be this: the dermal cranial skeleton of vertebrates, whether it takes the form of a bony skull or of the dorsal plates of a cephalaspid or a pteraspid is, in all cases, not cuticular, i.e. is not an external formation of the epidermal cells, but is formed in tissue of the nature of connective tissue underlying the epidermis. On the contrary, the hard part of the head-carapace of the palæostracan is an external formation of the epidermal cells. ”

“ We now come to Bone, a tissue confined to the vertebrata, and typically shown only in the higher types. As we descend in the scale from birds and mammals to lizards, amphibia (frogs and toads) and fish, we find cartilage continually more important, and the bony constituent of the skeleton correspondingly less so. In such a type as the dog-fish, the skeleton is entirely cartilaginous, bone only occurs in connection with the animal's scales; it must have been in connection with scales that bone first appeared in the vertebrate sub-kingdom. ”

“ It seems rather constant in each species, so that all the pieces of the skeleton of one specimen possess either four or six or eight lateral meshes, &c. But sometimes individual irregularities occur. In the majority of species each skeleton-piece is armed with spines. Usually a radial horizontal spine starts centrifugally from each corner of the basal ring, and on the side of this a small tooth or thorn often starts centripetally or downwards. ”

“ The long curved spines (s, s, s) , are a very curious feature of the appendage and the most marked character of the genus and species. They are articulated to the posterior margin of the joints, as the latter rest flattened out in the slate or shale, and there is no evidence but that they form a single series as shown in the specimen and in the drawing, figure 2. Each spine is constricted a little near its base, forming a rounded end or point of articulation; from this well out toward their pointed termination they retain an average width curving gently backward and inward. ”