Naturally, it is among the free living forms that the parapodium is best developed, and least developed among the tubicolous belongs typically a long tentacle, the cirrus, which 'r podium or neuropodium, and may be developed into an arborescent gill or into a flat scale-like process, A the elytron (in Polynoe, &c.).
U, The otocyst attached to the Ctenidium (gill-plume).
The gill-plume,which in A plysia is the typicalMolluscan ctenidium, is seen in fig.
The most noteworthy waterfalls are - Scale Force (Dano-Norwegian fors, foss), besidesCrummock, Lodore near Derwentwater, Dungeon Gill Force, beside Langdale, Dalegarth Force in Eskdale, Aira near Ullswater, sung by Wordsworth, Stock Gill Force and Rydal Falls near Ambleside.
"SIR DAVID GILL (1843-1914), British astronomer, was born in Aberdeenshire June 12 18 4 3 and educated at the university of Aberdeen.
The gill-lamellae of Patella are processes of the mantle comparable with the plait-like folds often observed on the roof of the branchial chamber in other Gastropoda (e.g.
4, d, the large branchial vein of Patella bringing blood from the gill-series to the heart is seen; where it crosses the series of lamellae there is a short interval devoid of lamellae.
Limpet, and that of the g ' nerves which pass from the visceral loop of Haliotis to the olfactory patch or osphradium, which lies in immediate relation on the right and on the left side to the right and left gill-plumes (ctenidia) respectively.
D, Left (archaic right) gill e, Reflected mantle-flap. fi, The fissure or hole in the mantle-flap traversed by the longitudinal incision.
Br, Ctenidium (gill-plume).
The heart c lying in the pericardium is seen in close proximity to the renal organ, and consists of a single auricle receiving blood from the gill, and of a single ventricle which pumps it through the body by an anterior and posterior aorta.
The surface x of the mantle between the rectum and the gill-plume is thrown into folds which in many sea-snails (whelks or Buccinidae, &c.) are very strongly developed.
The single gill-plume br lies to the left of the median line in natural position.
The minute structure of the epithelium which clothes it, as well as the origin of the nerve which is distributed to the parabranchia, proves it to be the same organ which is found universally in molluscs at the base of each gill-plume, and tests the indrawn current of water by the sense of ?,g smell.
I, Ctenidium (gill-plume).
34.-Female Janthina, with egg-float (a) attached to the foot; b, egg-capsules; c, ctenidium (gill-plume); d, cephalic tentacles.
Mantle-skirt, allowing the g, Gill-plume (ctenidium).
In front, near the anterior attachment of the gill-plume, is the osphradium (olfactory organ) dis h covered by J.
A, mouth; b, cephalic tentacle; h, gill (ctenidium).
Thus the base of the gill passes in a slanting direction across the right-hand side of the kidney, the posterior end being dorsal to the apex of the gland, and the anterior end ventral to the right-hand corner.
- Nymph of May-fly (Chloeon dipterum), with wing rudiments (a) and tracheal gill-plates (b, b).
Thus the whole of the Pulmonata (which breathe air, are destitute of gill-plumes and operculum and have a complicated hermaphrodite reproductive system) are either snails or slugs.
The land-snails which have no gill-plume in the mantle-chamber and breathe air, but have the sexes separated, and possess an operculum, belong to the orders Aspidobranchia and Pectinibranchia, and constitute the families Helicinidae, Proserpinidae, Hydrocenidae, Cyclophoridae, Cyclostomatidae and Aciculidae.
These all possess a fully developed gill-plume and are typical Pectinibranchs of the sub-order Taenioglossa, most of the members of which are marine.
Valvata is common in fresh waters throughout Britain; the gill when the animal is expanded is protruded beyond the mantle-chamber.
Gill, and carried in 1907 within 70 m.
In 1865 Kowalevsky discovered that the organs of respiration consist of numerous pairs of gill-slits leading from the digestive canal through the thickness of the body-wall to the exterior.
In 1883-1886 Bateson showed by his embryological researches that the Enteropneusta exhibit chordate (vertebrate) affinities in respect of the coelomic, skeletal and nervous systems as well as in regard to the respiratory system, and, further, that the gill-slits are formed upon a plan similar to that of the gillslits of Amphioxus, being subdivided by tongue-bars which depend from the dorsal borders of the slits.
The possession of gill-slits is as interesting a feature in the organization of Balanoglossus as is the presence of tracheae in Peripatus.
These gill-slits occupy a variable extent of the anterior portion of the trunk, commencing immediately behind the collartrunk septum.
The gill-slits may be stated briefly as follows: - (a) the presence of two kinds of branchial bars in all species and also of small cross bars (synapticula) in many species; (s) numerous gill slits, from forty to more 1 - _ than a hundred pairs; (y) the addition of new gill-slits by fresh perforation at the posterior end of the pharynx throughout life.
The difference between the gill-books of Limulus and the lung-books of Scorpio depends on the fact that the latter are adapted to aerial respiration, while the former serve for aquatic respiration.
Had the internal contacts alone been used, which many astronomers would have considered the proper course, the result would have been 8.776" In 1877 Sir David Gill organized an expedition to the island of Ascension to observe the parallax of Mars with the heliometer.
The failure of the method based on transits of Venus led to an international effort carried out on the initiative of Sir David Gill to measure the parallax by observations on those minor planets which approach nearest the earth.
The instruments used were heliometers, the construction and use of which had been greatly improved, largely through the efforts of Gill himself.
These observations.were worked up and discussed by Gill with great elaboration in the Annals of the Cape Observatory, vols.
This last value agrees very closely with a determination made by Gill at the Cape of Good Hope, and most other recent determinations give values exceeding 20.50".
The chief differences are, that (a) the tongue-bar is the essential vm, organ of the gill-slit in Balanoglossus, and exceeds FIG.
In most species of Balanoglossus each gill-slit may be said to open into its own atrial chamber or gill-pouch; this in its turn opens to the exterior by a minute gill-pore.
There are, therefore, as many gill-pouches as there are gill-slits and as many gill-pores as pouches.
The gill-pores occur on each side of the dorsal aspect of the worm in a longitudinal series at the base of a shallow groove, the branchial groove.