On the middle segment of the body dorsal and ventral folds, destined to form the mantle lobes, make their appearance, and on the latter two pairs of bundles of setae are present (fig.
These setae are usually placed at the sides of the anterior part of the body, immediately behind the head, and also sometimes on the posterior parts of the body.
Shorter setae are also lodged on the edge of the dorsal lobe.
The layer from which the sacks for the setae and the segmental organs spring is still doubtful.
The setae together with the mantle folds grow greatly, and the setae resemble in appearance the provisional setae of many Chaetopods (fig.
Provisional setae do not appear to be formed in the lobed embryos of Thecidium and Terebratulina, but they appear at a later stage at the edge of the mantle in the latter form.
It resembles, in fact, a mesotrochal larval Chaetopod with provisional setae (vide Chapter on Chaetopoda).
The dorsally situated processes with provisional setae last for some time, but finally disappear.
Agassiz has pointed out that setae of this kind, though not found in existing Chaetopods, are characteristic of the fossil forms.
Of the further external changes the most important are (1) the early appearance round the anal end of the body of a ring of bristles; and (2) the appearance of a pair of ventralsetae in the anterior part of the body.
In both of these feet Chaetopod-like setae were present, which in the hinder pair were simple fine bristles without a terminal hook.
Setae of this kind are found in chaetopod-like larvae of some Brachiopods (Argiope, fig.
A very considerable number of Chaetopod larvae are provided with very long provisional setae (figs.
In many cases thesetae appear before there are any other visible rudiments of the feet (e.
Antennae and setae also were affected and micrococci were recovered from the feces.
Their natatory respiratory abdominal laminae seem copied from the former, and their anal diverging setae from the latter[407].
Polyphagous; hexapod; antenniferous: body with segments of trunk distinctly marked; anus often furnished with setae or mucro.
The terminal setae of the second pair of antennae project between the cheliferous feet.
The spatuliform caudal lamina bears from five to six pairs of setae on its hinder margin.
The tail, of very variable form, always bears THREE pairs of setae at its hinder margin.
The sole distinction, that in the latter there are only 3 setae at the end of the outer branch, whilst in the Cirripedia there are 4 on the first and 5 on the following natatory feet, may be due to an error on my part.
On the abdomen six pairs of powerful biramose natatory feet with long setae have been formed beneath the Nauplius-skin, and behind these are two short, setigerous caudal appendages (Figure 58).
The arrangement of the processes of the carapace, and, still more, the similar number of the caudal setae in the most different Zoeae of Crabs (Figures 19 to 23) prove this.
The abdomen possesses three rows of setae on each side above the spiracles.
Two setae are located on the vertex and two on the occupit of head.
Vein R{4+5} without setaeat the base; palpi about as long as the proboscis.
Venezuela has bare genae, oralsetae not ascending; tibiae villose; claws short in both sexes; Sarconesia Bigot with the species S.
Middle tibia with one or more prominent setae on the inner (flexor) surface beyond the middle, or inner surface very hairy.
Java, has the setae on the facial ridges rising to the base of the antennae and has median marginal macrochaetae on the abdominal segments two to four: Blepharicnema Macq.
The tarsus of the fourth pair of legs has a number of curved setae in a single series.
Setae on the exterior surface of the hind tibiae wanting (except in Limnaricia and Coenosites), lower squama not broadened to the margin of the scutellum.
First anal vein short, second anal suddenly flexed upwards; hind tibiae each with one or two strongsetae on the extensor surface.
In Echiurus and Thalassema the same vessel forms a ring round a stout muscle, which connects the bases of the two ventral setae before passing to surround the intestine.
No other member of the group is known to have any trace of setae or parapodia at any stage of development.
That belonging to the third shows some long setae and a trace of the shaft, while the one on the fourth appendage (third coxopodite) has a portion of a broad shaft and a number of long setae.
The setae in turn became modified from their original simple cylindrical shape to form the wide, thin, blade-like filaments of Cryptolithus and Ceraurus.
Both the exopodite and endopodite are shorter than in the trilobites, but bear setae and spines.
The same condition occurs in specimens of Marrella when the setae of several exopodites are matted against each other.
Yet all gradations are found among the sections, from the long setae to the short dots.
A few fortunately located sections in a more nearly horizontal plane might cut the setae and occasionally the shaft of one or more exopodites in the longitudinal plane, and the resulting effect would produce the so-called "epipodites.
Several sections have already been illustrated showing sections across the setae of the exopodites (pl.
To the present writer it seems probable that the chief function was that of acting as gills, for which the numerous thin, flattened or blade-like setae are particularly adapted.
If these series of spots are interpreted on the basis of the known structure of Triarthrus, they are of course a series of sections through the setae of the exopodites.
It is oval in form, broken at the end toward the axial lobe, and has exceedingly minute short setae on the posterior margin.
The setae appear from the sections to have been more or less blade-shaped and to have overlapped, as do those of the exopodites of Cryptolithus.
The setae stand at right angles to the shaft, and on a portion of it 0.
The setae do not diverge from the shaft at a right angle as on the dorsal side of this same specimen, but at an acute angle, indicating that they were not rigid.
As in Arthropoda, the hairs orsetae on the surface of the body are important organs of sense and are variously modified for special sensory functions.
In the majority of the Decapoda there is a saccular invagination of the integument in the basal segment of the antennular peduncle having on its inner surface "auditory" setae of the type just described.
When feathered or provided with secondary barbs the setae will respond to movements or vibrations in the surrounding water, and have been supposed to have an auditory function.
Setae are only present in the genus Acanthobdella.
In all the figures the nephridial pores are indicated by dots and the setae by strokes.
The peristomium has no setae, and the setae generally are hair-like or uncinate, often forming almost complete rings.
In it the hairs are confined to the dorsal middle line and the creeping setae are hooked, of a finer structure than in Chaetosoma, and situated so far forward that the vagina opens amongst them.
There are no setae and apparently only two pairs of nephridia, of which the anterior pair open commonly by a common pore on the third segment after the head, whose segments have not been accurately enumerated.
The genital ducts are limited to one segment (the 8th in Capitella capitata), and there are genital setae on this and the next segment.
The setae are invariably formed each within an epidermic cell, and they are sheathed in involutions of the epidermis.
The absence of setae--save in Acanthobdella, where five of the anterior segments possess each four pairs of setae with reserve setae placed close behind them (fig.
The absence of setae and the great secondary annulation render the mapping of the segments a subject of some difficulty.
Setae always present and often very large, much varied in form and very numerous, borne by the dorsal and ventral parapodia (when present).
Alma is noteworthy for the facts that the male pores are borne upon long processes of the body which bear specially modified setae and that one species at any rate has gills.
In Onychochaeta the setae on the last segments of the body are very much enlarged and thus form a more effective means of holding on to the soil than is possessed by other species.
For the restriction of the setae to the ventral surface obviously favours progression upon a surface and not through a medium.
For the setae of each segment are increased to a large number much exceeding eight.
The setae of Dichogaster are sometimes ornamented, while in Pheretima houlleti the clitellar setae are different from those upon the other segments.
They have too very often glands connected with the enlarged setae already mentioned which are however (in the genus Kynotus at any rate) usually in front of the clitellum.
Each of these except the first has eight setae which for the first few segments of their occurrence are disposed in four pairs in the usual fashion.
On segment XIV are a pair of very minute pores a little in front of the ventralmost setae and thus very near together.
A marked feature of this family is that the dorsal bundles of setaedo not always begin like the ventral setae upon the second segment of the body.
Wings two; the posterior pair represented by two minute clubbed appendages termed poisers; mouth a suctorial tube formed by an elongation of the labium, enclosing within it a variable number of setae answering to the mandibles, &c.
In a few hours, however, a second moult occurs, the wings gaining additional size and beauty, and the anal setae becoming very much more elongated than before (Fig.
How many setae are there on each segment and what is their disposition?
Dorsal setae of the usual two types of which the upper are much fewer spatulate setae in two series with distal expansion broad and wings asymmetrical, tip short.
Like Phyllocomus in lacking tentacles and postbranchial spines, in bearing fifteen pairs of fasciae of capillary setae and four pairs of branchiae.
It differs from the former genus in having only composite setae and in having these of the ordinary structure, the appendage of a simple, fringed form not covered by a membrane.
Notopodia reduced to small lobes at base of neuropodia above, these lobes smooth, bearing no emergent setae in the type.
Most dorsal thoracic setae in each fascicle long and finely pointed with wings narrow; the ventral setae much more numerous, shorter, spatulate, with fine tip.
The setae of the other series are more curved than in robusta and are abruptly contracted farther from the body, the contraction stronger but the one edge similarly roughened or denticlated with cross lines.
The notopodial setae fine, numerous, the longer ones not falling much short of or reaching the ends of the neuropodials.
They extend out far laterally so as wholly to overlap the parapodia proper though the ends of the setae and notocirri extend beyond the edges.
Tentacular cirri resembling median tentacle in form, being narrowed distad with subapical enlargement slight; one or two fine setae emerging from a small nodule at distal end of parapodium proximad of tentacular cirrus.
These coarse setae are not at all clavate as in elongata and are not roughened or cross-ridged above the curve as in robusta; the terminal region above the curve longer than in the later species.
Parapodia uniramous with setae all compound, or in the epitokous phase with long simple natatory setae in notopodia of middle region of body.
The middle region of the body bears notopodeal fasciae of long, fine, simple, natatory setae in addition to the compound neuropodials.
The neuropodial setae of the anterior region are arranged in three subvertical series and form a patch twice as high (dorsoventrally) as long (cephalocaudally).
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "setae" in a variety of sentences. We hope that you will now be able to make sentences using this word.
