Seta (zoology)

“ The upper and outer extremity of the vibraculum is bifid, and to the inner horn is articulated the seta, and from the notch between the two horns there is continued nearly, if not quite, to the inner extremity of the organ, and along its upper border, a shallow groove, in which is lodged the seta when in a state of rest. In most species the seta is serrated with distant teeth on one side.
Where there are more than two rows of cells, the marginal cells differ in conformation from the central.
As in Scrupocellaria, the opening of the cell is sometimes protected by a pedunculate operculum. ”

“ As we have already noticed, there is a considerable diversity among recent species, both as regards habitat and habit; in the anatomy of the stem also corresponding variations occur within the limits of a well-defined generic type of stele. In species with creeping stems, such as L. clavatum [96] , the stele exhibits an arrangement of vascular tissue characteristic of the plagiotropic forms. The xylem consists of more or less horizontal plates of scalariform tracheae, each surrounded by small-celled parenchyma, alternating with bands or groups of somewhat ill-defined phloem. ”

“ Setae all simple, limbate, in a single series of mostly six in the middle region of the body. Setae with the usual double or sigmoidal curve over the limbate part, the first bend or geniculation unusually strong, angular; tip becoming fine and hair-like. Body tapering caudad, pointed at the posterior end, ending in two blunt lobes. Number of segments in the type one hundred and ninety-one.
Length, 46 mm.; width, exclusive of parapodia, 2 mm. ”

“ The landowner may erect his cattle-pound on one side of the stream in perfect security, although the opposite bank may resound with the hum of swarms of these insects. When the natives, who are acquainted with the localities in which the tsetse-fly abides, are compelled, as they constantly are, to shift their ground, and, in changing their pastures, to transgress254 upon the district of the tsetse, they usually select the moonlight nights of winter, when the insect, during the quiet hours of the cold season, is not likely to molest their charge. ”

“ The central hydrom strand in the seta of the sporogonium of most mosses has already been alluded to. Besides this there is usually a living conducting tissue, sometimes differentiated as leptom, forming a mantle round the hydrom, and bounded externally by a more or less well-differentiated endodermis, abutting on an irregularly cylindrical lacuna; the latter separates the central conducting cylinder from the cortex of the seta, which, like the cortex of the gametophyte stem, is usually differentiated into an outer thick-walled stereom and an inner starchy parenchyma. ”

“ A third expedition was successful, although the whole party came near perishing for want of water, and their cattle, which had been bitten by the 'Tsetse', died.
This insect—the 'Glossina moritans' of the naturalists—deserves a special paragraph. It is a brown insect about as large as our common house-fly, with three or four yellow bars across its hinder part. A lively, buzzing, harmless-looking fellow is the tsetse. Its bite produces a slight itching similar to that caused by the mosquito, and in the case of men and some species of animals no further ill effects follow. ”

“ In size the tsetse is somewhat less than the common blue fly that settles on meat, but its wings are longer. Yet, though so small and insignificant in appearance, its bite carries with it a poison equal to that of the most deadly reptile. Many is the traveler who, from his draft-oxen and horses having been destroyed by this pestiferous insect, has not only had the object of his journey completely marred, but his personal safety endangered by the loss of his means of conveyance. ”

“ The tsetse-flies reproduce differently from all other Muscidæ. The female produces at each birth a single full-grown larva, which is retained within the oviduct and there nourished by the secretion of special glands, and on being born crawls to some hiding place and at once becomes a puparium. ”

“ Setae.—These chitinous, rod-like, rarely squat and then hook-like structures are found in the majority of the Chaetopoda, being absent only in certain Archiannelida, most leeches, and a very few Oligochaeta. They exist in the Brachiopoda (which are probably not unrelated to the Chaetopoda) , but otherwise are absolutely distinctive of the Chaetopods. The setae are invariably formed each within an epidermic cell, and they are sheathed in involutions of the epidermis. Their shape and size varies greatly and is often of use in classification. ”

“ The tsetse-flies develop in a very different way from most insects. The female does not deposit her eggs, but a single one develops to the fully grown larval condition before being deposited. This larva soon pupates in the shade beneath the brush bordering the water where it has been dropped by the parent fly, and later emerges in the winged adult condition. The pupa? require such moist shade, and it is apparently for this reason alone that the flies never occur away from the immediate vicinity of the water. ”

“ The Cete, or Whales, although they resemble fishes in external appearance, are ranged very properly amongst the Mammalia, having warm blood, similar lungs, teats, &c. Instead of feet, they are provided with pectoral fins, and a horizontally flattened tail, fitted for swimming. They have no hair. The teeth are in some species cartilaginous, and in others bony. Instead of nostrils, they have a tubular opening on the top of the head, through which they occasionally spout water. They live entirely in the sea; feeding on the soft marine animals and vegetables. ”

“ I lay myself down [in death] , and I am born daily.
I am Seta at the confines of the earth. I lay myself down [in death] , I restore myself and I renew myself daily.
Note. Se-ta , literally Filius terrae, is a common noun signifyingsignifying an earth-worm. It is applied to the Sun as rising out of the earth. There are several pictures at Denderah representing the Sun-god Hor-sam-ta in the form of the worm rising out of the Lotus of Dawn. See pl. xxiii, from Mariette, Dend. I, 47 and 48.
CHAPTER LXXXVIII. ”

“ Setae always present and often very large, much varied in form and very numerous, borne by the dorsal and ventral parapodia (when present) . The prostomium and the segments generally often bear processes sensory and branchial. Eyes often present and comparatively complicated in structure. Clitellum not present as a definite organ, as in Oligochaeta. The anus is mostly terminal, and there are no anterior and posterior suckers. Nervous system often imbedded in the epidermis. Vascular system generally present forming a closed system of tubes. ”

“ Under the influence of the following first genial spring weather, the larva is transmuted into the pupa, and the active little imago comes forth upon the settlement of our variable spring, in the merry days of June, and thus is perpetuated the circle of its existence, but which is sometimes abridged by its special parasite, the pretty little Stelis octomaculata. Many of the species in the males are distinguished by a peculiar armature of the apex of the abdomen ”

“ Whilst rowing to these caves we had seen one black guillemot, or "tysty," flying over the sea with a fish in its bill, and another swimming with a young one by its side. The latter was of a greyish colour, and about a third smaller than the parent bird, which in shape and movements it closely resembled. These birds, therefore, breed in the Shetlands—a fact well known before, I believe; but I like to rediscover things. Another and more interesting thing that we saw was a seal swimming very fast, and leaping, at intervals, out of the water. ”

“ At maturity the seta elongates rapidly, and the wall of the capsule splits more or less completely into four valves, allowing the elaters and spores to escape. In the Jubuloideae, which in other respects form a well-marked group, the seta is short and the elaters extend from the upper part of the capsule to the base; at dehiscence they remain fixed to the valves into which the capsule splits. The germinating spore usually forms a short filament, but in other cases a flat plate of cells growing by a two-sided apical cell is first formed (Radula, Lejeunea) . ”

“ The tsetse flies rapidly and directly to the objects it seeks, and must have a keen sense of smell or sight, or both, making straight for its prey, and being most persistent in its attacks. The buzzing which it produces when flying is peculiar, and easily recognized again when once heard. ”

“ The poison-germ, contained in a bulb at the root of the proboscis, seems capable, although very minute in quantity, of reproducing itself, for the blood after death by tsetse is very small in quantity, and scarcely stains the hands in dissection. I shall have by-and-by to mention another insect, which by the same operation produces in the human subject both vomiting and purging.
The mule, ass, and goat enjoy the same immunity from the tsetse as man and the game. ”

“ The species of the genus Setina have Alpine forms which agree in possessing a characteristic extension of the black pigment to form radiating junctions between the spots on the wings. Speyer, who discussed the interrelations of these forms in detail, [22] lays stress on the absence of genuine transitional forms between aurita and the variety ramosa. Both are mountain insects but ramosa extends to levels higher than that at which aurita ceases, which is about 4,000 feet. The two forms are often found flying together. ”

“ The sleeping sickness of man, in Africa, has also been supposed to be directly inoculated by one, or several, species of tsetse-flies. It is now known that the fly may convey the disease for a short time after feeding, but that there is then a latent period of from fourteen to twenty-one days, after which it again becomes infectious. This indicates that in the meantime the parasite has been undergoing some phase of its life-cycle and that the fly serves as an intermediate host. ”

“ The points of disagreement are many, and such as to make it entirely improbable that this fly is the true tsetse, though my men unanimously stated that its bite was fatal to horses as well as to donkeys. A descriptive abstract of the tsetse would read thus: "Not much larger than a common house-fly, nearly of the same brown colour as the honey-bee. After-part of the body has yellow bars across it. It has a peculiar buzz, and its bite is death to the horse, ox, and dog. On man the bite has no effect, neither has it on wild animals. ”

“ An insect, little bigger than the common fly of England, but whose sting is deadly as the bite of rattle-snake or cobra-di-capello; fortunately not to man himself, but to man’s best friends in the animal world—dogs, horses, cattle, and sheep (Note 1) . So when Andries Rynwald called out the name of the venomous creature, Piet Van Dorn and his brother had instant and clear comprehension why the camp was being so abruptly abandoned. The tsetse had made its appearance there; in flight lay the sole chance of saving the stock, and even this might be too late. ”

“ Similarly, an area in which animals of a particular species might thrive, is not colonized by them because they are not fleet enough to escape some beast of prey inhabiting this area, or because the area is infested by some insect which destroys them, as the tsetse destroys the cattle in parts of Africa. ”

“ Diagnosis.—Size medium for the species, tail relatively long; average and extreme measurements of 17 specimens from the type locality are: total length, 128.4 (122-138) ; tail, 57.8 (53-66) ; hind foot, 15.1 (14-16) . Color dark in summer and winter.
Comparisons.—For comparison with S. v. setosus see account of that subspecies. Larger and darker than S. v. obscurus with which it intergrades east of the humid coastal region; larger and darker than S. v. alascensis with which [Pg 38] it intergrades in the Lynn Canal area; larger and darker than S. v. ”

“ Probably those organs which have the greatest effect in modifying the shape of the body are the septa, for we find in the long, free-swimming worms that these are regularly present throughout the body, and external "segmentation" of the body is well marked. In burrowing and tubicolous forms the septa are frequently incompletely developed, or more or fewer may be absent; and the body becomes less distinctly segmented externally, tends to vary greatly in diameter during movement, or becomes plumper. ”

“ In a section of this species in the Williamson Collection [1161] the long axis of the stele has a length of 5 mm. and the diameter of the stem as a whole is 2·5 cm. The greater part of the extra-stelar tissue consists of large parenchymatous cells passing near the periphery into a band of darker and thicker-walled tissue.
Reniform vascular strands traverse the cortex in an obliquely ascending course on their way to the leaves, also smaller bundles, some of which are given off directly from the stele, while others are branches of the petiole vascular strands. ”

“ The Indian species do not always plaster up their holes, and the American apparently never do so. Sitella forms a curious funnel-shaped nest with a very thin rim, in forks or on branches, using as materials bark, moss, down, cobwebs, and lichens, the bark being applied externally like shingles. The three or four greenish or bluish-white eggs, with blackish, grey, or lilac markings, are very unlike those of Sitta, which are white, with fine pinkish-red and lilac spots or blotches, and number from five to eight. ”