39) have jointed, flexible palps, feelers - often of excessive length - with a short basal segment, and the three terminal segments forming a club, and, in some genera, larvae with legs.
In male beetles, however, the two pairs of genital processes (paramera) belonging to the ninth abdominal segment are always present, though sometimes reduced.
As in the Oligochaeta the peristomial segment is often without setae; but this character is not by any means so constant as in the Oligochaeta.
In many of those ants whose third abdominal segment forms a second " node," the basal dorsal region of the fourth segment is traversed by a large number of very fine transverse striations; over these the sharp hinder edge of the third segment can be scraped to and fro, and the result is a stridulating organ which gives rise to a note of very high pitch.
Apical cell, p. Wall marking limit between the plerome k, initial segment of root-cap. P and the pleriblem Pb.
Turning to the thorax we find that the first segment (prothorax) is distinct and free, with a wide dorsal sclerite.
R, Optical section of leptoid (sieve-tube segment) of Phanerogam, with two proteid (companion) cells.
In these ants the difference between the large, heavy, winged males and females, and the small, long-legged, active workers, is so great, that various forms of the same species have been often referred to distinct genera; in Eciton, for example, the female has a single petiolate abdominal segment, the worker two.
It is, however, always possible to recognize a head, which consists at least of the peristomial segment with a forward projection of the same, the prostomium.
(7) On Floating Bodies (Peri okoumenon) is a treatise in two books, the first of which establishes the general principles of hydrostatics, and the second discusses with the greatest completeness the positions of rest and stability of a right segment of a paraboloid of revolution floating in a fluid.
3, 4), and of constructing a segment of a sphere similar to one given segment and having (a) its volume, (b) its surface, equal to that of another (5, 6).
A tissue mother-cell of the xylem may, in the most advanced types of Dicotyledons, give rise to(I) a tracheid; (2) a segment of a vessel; (3) a xylem-fibre; or (4) a vertical file of xylem-parenchyma cells.
This remark applies to the finding of the area of a parabolic segment (mechanical solution) and of a spiral, the surface and volume of a sphere and of a segment thereof, and the volume of any segments of the solids of revolution of the second degree.
The second book in ten propositions is devoted to the finding the centres of gravity (I) of a parabolic segment, (2) of the area included between any two parallel chords and the portions of the curve intercepted by them.
The young insect resembles its parent in most points, but the head is disproportionately large; the anterior abdominal spiracles are on the second segment instead of on the first, and the foot has only a single segment.
I, 4) the abdomen is cylindrical, the female is provided with a ventral ovipositor and has the terminal abdominal segment conical; the corresponding segment in the male is usually bluntly rounded.
The general graphy, principle Arms a and arrangement b, one at eachstation and d B, are connected to the line wire, and are made to rotate simultaneously over metallic segments, 3, 4, and I', 3', 4', at the two stations, so that when the arm a is on segment i at A, then b is on segment I' at B, and so on.
This consists of a few xylem elements, e a a segment of phloem, pericycle, and usually an arc of h~s endodermis, which closes round the bundle as it detaches ~
A tissue mother-cell of the phloem may give rise to (i) a segment of a sieve-tube with its companion cell or cells; (2) a phloem fibre; (3) a single phloem-parenchyma (cambiform) cell, or a ve~rtical file of short parenchyma cells.
- The Rhynchophora are a group of beetles easily recognized by the elongation of the head into a beak or snout, which carries the feelers at its sides and the jaws at its tip. The third tarsal segment is broad and bi-lobed, and the fourth is so small that the feet seem to be only four-segmented.
The insects of this order have mandibles adapted for biting, and two pairs of membranous wings are usually present; the first abdominal segment (propodeum) becomes closely associated with the fore-body (thorax), of which it appears to form a part.
The fourth abdominal segment is often very large, and forms the greater part of the hind-body; this segment is markedly constricted at its basal (forward) end, where it is embraced by the small third segment.
Biisgen that the sweet secretion (honey-dew) of the aphids is not derived, as generally believed, from the paired cornicles on the fifth abdominal segment, but from the intestine, whence it exudes in drops and is swallowed by the ants.
On the other hand, in certain Polychaeta the bundles of setae are so extensive that they nearly form a complete circle surrounding the body; and in the Oligochaet genus Perichaeta (=Pheretima), and some allies, there is actually a complete circle of setae in each segment broken only by minute gaps, one dorsal, the other ventral.
In the latter case each segment of the solenostele frequently resembles a Dktyosteb.
Antennal segment s form a distinct club.
The head of an ant carries a pair of elbowed feelers, each consisting of a minute basal and an elongate second segment, forming the stalk or "scape," while from eight to eleven short segments make up the terminal "flagellum."
Oviducts of Oligochaeta, sperm ducts of Phreoryctes, the coelomoducts occupy, like the nephridia, two segments, the funnel opening into that in front of the segment which carries the external pore.
The more complete replacements, such as the nephridia of the genital segment of Tubifex by a subsequently formed genital duct, may be compared with the succession of the nesonephros to the pronephros in vertebrates, and of the metanephros to the mesonephros in the higher vertebrates..
The funnel, which is not large, appears to open, as a rule at least, into the segment in front of that which bears the external orifice.
It is noteworthy that in this family only among the Polychaeta, the nephridia are not restricted to a single pair in each segment; so that the older view that the gonad ducts are metamorphosed nephridia is not at variance with the anatomical facts which have been just stated.