The number is significant, since it agrees with that found in Edriophthalmous Crustacea, and assigns the labium of the Hexapod to the same somite numerically as that which carries the labium-like maxillipedes of those Crustacea.
A pair of coelomoducts is developed in every somiteincluding the prosthomere, in which alone it atrophies in later development.
Whether the primitive tracheal system of Hexapoda was a closed one or open by serial stigmata in every somite remains at present doubtful, but the intimate relation of the system to the wings and tracheal gills cannot be overlooked.
Only one somite following the first post-oral or mandibular segment has its appendages modified as jaws.
II, Coelom of the second somite which carries the mandibles (hence deuterognathous).
The head shows two jaw-bearing somites besides the mandibular somite (V, VI, in fig.
In Crustacea the fourth or mandibular somite never has less than the two following somites associated with it by the adaptation of their appendages as jaws, and the ankylosis of their terga with that of the prosthomeres.
The adhesion of a greater or less number of somites to the buccal somite posteriorly (opisthomeres) is a matter of importance, but of minor importance, in the theory and history of the Arthropod head.
The third somite as well as the second develops a pair of parapodial jaws; the first somite is a prosthomere carrying jointed antennae.
With a single pair of parapodial jaws carried by the somite which is perforated by the mouth; this is not the first somite, but the second.
The genital apertures are placed on the first somite of the second tagma or mesosoma.
B) it separates from the rest of the somite and commences to extend ventrally, thus covering over the pronephros and its duct, until finally (Fig.
The development of a somite for the procephalic lobes is similar to what has been described by Kleinenberg for Lumbricus (p.
The two cavities in the cephalic commissure unite dorsally, but ventrally open into the first somite of the trunk.
In the larval development of the more primitive Crustacea, the number of somites, at first small, increases by the successive appearance of new somites between the last-formed somite and the terminal region which bears the anus.
T, telson, having the uropods or appendages of the last abdominal somite spread out on either side of it, forming the "tail-fan.
Apart from the possible existence of an ocular somite corresponding to the eyes (the morphological nature of which is discussed below), the smallest number of head-somites so united in any Crustacean is five.
The typical form of a somite is well seen, for example, in the segments which make up the abdomen or "tail" of a lobster or crayfish (fig.
Frequently, however, this exoskeletal somite may be differentiated into various regions.
Abdominal Somiteof a Lobster, separated and viewed from in front.
The seventh, and sometimes the eighth, leg-bearing somite is present and has its leg-like appendages fully developed.
The simple identification of somite with somite in Limulus and Scorpio seemed to be threatened by this discovery.
The dotted line on somite I indicates the position of the genital operculum which was probably provided with branchial lamellae.
VIIgo, The genitalsomite or first somite of the mesosoma with the genital operculum (a fused pair of limbs).
Ventral surface of the anterior region of the opisthosoma, the first somite being pushed upwards and forwards so as to expose the subjacent structures.
There is no doubt that these are parapodial or limb appendages, carrying numerous imbricated secondary processes, and therefore comparable in essential structure to the leaf-bearing plates of the second mesosomatic somite of Limulus.
One of the lateral pieces of a somite of an insect.
In crustaceans: The part of the side of a somite external to the basal joint of each appendage.
The dorsal portion of an arthromere or somite of an articulate animal.
Spiracles are never present upon the anal, genital and last leg-bearing somites, and only rarely, as in Henicops, upon the somite bearing the legs of the first pair.
The exoskeletal elements of a typical somite consist of a dorsal plate or tergum, a ventral plate or sternum, a lateral or pleural membrane, often strengthened with chitinous sclerites, and a pair of appendages.
The tergal plate of the somite bearing the toxicognaths always remains distinct and separates the head-shield from the tergum of the first leg-bearing somite.
The genital somite is always small and sometimes retractile within the somite bearing the last pair of legs.
Tergal plate of somitebearing legs of the first pair.
The anterior portion of each somite is only partially cut off as a subsegment.
The sternal plates of all the jaw-bearing somites have disappeared, except in the case of the somite of the toxicognath, where it may be vestigial.
The tergal plate of the somite bearing the toxicognaths is suppressed, probably by fusion with the tergum of the first leg-bearing somite.
Each leg-bearing somite contains a distinct tergum and sternum, the number of sterna never exceeding that of the terga.
The color of the dorsum is blackish, with pale transverse lines in the intersegmental furrows and bisecting each somite which under the lens thus appears double.
The peristomium much longer than the prostomium than which it is also clearly wider and higher; entire second somite very short, not more than one-fourth as long as I.
The second branchia attached just caudad of the first on the caudal region of somite III.
Ventral tentacular cirrus of second somite of a thin or foliaceous and asymmetrical form.
First branchia on each side attached to second somite just in front and mesad of the first setigerous tubercle.
General color yellowish; each somite of anterior region crossed transversely by two fine complete lines of reddish brown color.
Peristomium forming a lower lip of but moderate length with straight anterior edge; scarcely twice as long as the second somite below.
The branchiae begin on the twenty-ninth setigerous somite and continue to about the one hundred and twenty-ninth, decreasing in size at the two ends of the series.
In front of this they remain a uniform distance apart, which is less than the length of a somite, forward to about the tenth somite from where the rows diverge gradually forward.
On each side of this groove it exhibits in each appendage-bearing somite a well-marked thickening, which gives in surface views the appearance of a slightly raised area (Pl.
Beneath the procephalic lobes the mesoblast has, in most respects, a constitution similar to that of a mesoblastic somite in the trunk.
Each mesoblastic somite is formed of a distinct somatic layer closely attached to the epiblast, and a thinner and less well-marked splanchnic layer.
Which somite of the crayfish is without appendages?
How are the somite shells arranged to protect the body during bending?
How many somites are there in a crayfish's body, if each somite bears only one pair of appendages, as many scientists believe?
Study the somite shells on every side and then state what there is in their construction which determines the direction and amount of their motion.
He divides each somite (segment) into eight pieces, grouped in pairs--viz.
In an early stage every somite has its tergal region divided into lateral halves, owing to the late completion of the body on this side.
All carefully performed experiments on the nervous system of Arthropoda have shown that each ganglion of the ventral chain is a motor centre, and in Insects a respiratory centre, for the somite to which it belongs.
Only one pair is functional at a time, but these are supposed to be survivors of a series of segmentally arranged organs, so that there might be a pair to each somite of a trilobite.
Embryologically they arise precisely like the legs, and each cercus contains a diverticulum of the mesoblastic somite precisely as is the case with the ambulatory legs and mouth parts.
The first somite arises close to the foremost extremity of the primitive streak, but the next is stated to arise in front of this, so that the first formed somite corresponds to the second permanent vertebra[63].
At the stage figured the head is well marked off from the trunk, but the first separation between the two regions was effected at an earlier period, on the appearance of the foremost somite (fig.
Each somite is composed of two layers--a somatic and a splanchnic--both formed of a single row of columnar cells.
In the course of further development it continues to constitute such a ridge as far as the eleventh somite (Sedgwick), but from this point it grows backwards in the space between the epiblast and mesoblast.
The increase in length of the body mainly takes place by growth in the region between the last mesoblastic somite and the end of the tail.
They are the foremost somites of the trunk, and those behind them continue to be added, like the segments in Chaetopods, between the last formed somite and the end of the body.
The anterior mesoblastic somite long retains its communication with the mesenteron, and was described by Max Schultze, and also at first by Kowalevsky, as a glandular organ.
One segmental tube makes its appearance for each somite (fig.
Below, the sternum of each somite is seen to be only a narrow bar, connected with those in front and behind by soft membrane, and there is no overlapping.
The telson is often absent, or, rather, it is coalesced with the last somiteof the abdomen.
There is no distinct carapace, but the last vestige of one may be indicated by the fact that the first thoracic somite is completely fused with the head.
There is no carapace, but, as in the Isopods, the first thoracic somite is fused with the head.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "somite" in a variety of sentences. We hope that you will now be able to make sentences using this word.
