Bd, Enlargement of the oesophagus, armed with chitinous teeth..
Sutures are stated to mark off some of these pieces, but in the proper sense of that term as applied to the skeletal structures of the Vertebrata, no sutures exist in the chitinous cuticle of Arthropods.
The body-wall is highly muscular and, except in a few probably specialized cases, possesses chitinous spines, the setae, which are secreted by the ectoderm and are embedded in pits of the skin.
In one subdivision of the leeches, the Gnathobdellidae, the mouth has three chitinous jaws which produce a triangular bite, though the action has been described as like that of a circular saw.
60), where the interspaces between the coenosarcal tubes are filled up with calcareous matter, or coenosteum, replacing the chitinous perisarc. The result is a stony, solid mass, which contributes to the building up of coral reefs.
The envelope is double, consisting of an external chitinous stratified shell, and an internal thin elastic membrane.
Trophosome polyps forming branching colonies of which the stem and main branches are thick and composed of a network of anastomosing coenosarcal tubes covered by a common ectoderm and supported by a thick chitinous perisarc; hydranths similar to those of Coryne; gonosome, sessile gonophores.
(After coralline may be regarded as a form of Moseley.) hydroid colony in which the coenosarc forms a felt-work ramifying in all planes, and in which the chitinous perisarc is replaced by a massive calcareous skeleton.
Ceratella stands in much the same relation to the Stylasteridae that Hydractinia does to the Milleporidae, in both cases the chitinous perisarc being replaced by the solid coenosteum to which the hydrocorallines owe the second half of their name.
The pneumato phore arises from the ectoderm as a pit or invagination, part of which forms a gas-secreting gland, while the rest gives rise to an air-sack lined by a chitinous cuticle.
The upper surface of the elytron is sharply folded inwards at intervals, so as to give rise to a regular series of external longitudinal furrows (striae) and to form a set of supports between the two chitinous layers forming the elytron.
Along the sutural border of the elytron, the chitinous lamella forms a tubular space within which are numerous glands.
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.
There are two chitinous jaws in the buccal cavity, a dorsal and a ventral, which are of specially complicated structure in Cirrodrilus.
Stomach generally provided with chitinous or calcified masticatory plates.
Margins of foot well developed; eyes superficial; three chitinous stomachal plates; shell external, with reduced spire.
As in other Gastropoda Anisopleura, this shell-sac may abnormally develop a plug of chitinous matter, but normally it flattens out and disappears, whilst the cap-like rudiment of the permanent shell is shed out from the dome-like surface of the visceral hump, in the centre of which the shell-sac existed for a brief period.
Shell largely chitinous, not spiral, its calcareous apex projecting through a small hole in the mantle.
Exoskeleton The outer cellular layer (ectoderm or " hypodermis ") of insects as of other Arthropods, secretes a chitinous cuticle which has to be periodically shed and renewed during the growth of the animal.
The regions of this cuticle have a markedly segmental arrangement, and the definite hardened pieces (sclerites) of the exoskeleton are in close contact with one another along linear sutures, or are united by regions of the cuticle which are less chitinous and more membranous, so as to permit freedom of movement.
The head is usually connected with the thorax by a distinct membranous neck, strengthened in the more generalized orders with small chitinous plates (cervical sclerites).
An air-tube consists of an epithelium of large polygonal cells with a thin basement-membrane externally and y a chitinous layer internally, the lastnamed being continuous with the outer cuticle.
The chitinous layer is usually strengthened by thread like thickenings which, in the region close to the outer opening of the tube, form a network enclosing polygonal areas, but which, through most of the tracheal system, are arranged spirally, the strengthening thread not forming a continuous spiral, but being interrupted after a few turns around the tube.
These spiracles have firm chitinous edges, and can be closed by valves moved by special muscles.
- A striking feature in the food-canal of the Hexapoda, as in other Arthropods, is the great extent of the " foregut " and " hind-gut," lined with a chitinous cuticle, continuous with the exoskeleton.
The " sclerites " that make up the skeleton of the insect (which skeleton, it should be remembered, is entirely external) are composed of this chitinous excretion.
Its integument is marked by a large number of transverse grooves simulating the segmentation of Annelids, and near the anterior extremity close to the mouth are two pairs of recurved chitinous hooks.
Again, the adult Pentastomum shows no trace of appendages, unless the two pairs of chitinous hooks are to be regarded as the vestiges of jaws or ambulatory limbs.
The free edges of the mantle often bear chitinous bristles or setae which project beyond the shell.
The chitinous chaetae have their origin in special ectodermal pits, at the base of which is one large cell which is thought to secrete the chaeta, as in Chaetopods.
XIl the free surfaces of the adjacent lamellae being --- covered with a very delicate chitinous cuticle ?,' Xlll which is drawn out into delicate hairs and .
The unsegmented dense chitinous sternal plate of the metasoma (XIII to XVIII) is not removed.
It consists of a single layer of cells, continuous with those which secrete the general chitinous covering of the prosoma.
They are at the same time both optic nerve-end cells, that is to say, retina cells, and corneagen cells or secretors of the chitinous lens-like cornea.
(From Lankester, loc. cit.) forming a star-like chitinous centre in section, each lateral eye of Scorpio has several rhabdoms of five or less rhabdomeres, indicating that the Limulus lateral eye-unit is more specialized than the detached lateral eyelet of Scorpio, so as to present a coincidence of one lens with one rhabdom.
Pmst, The promesosternal sclerite or chitinous plate, unpaired.
- Section through a portion of the lateral eye of Limulus, showing three ommatidia - A, B and C. hyp, The epidermic cell-layer (so-called hypodermis), the cells of which increase in volume below each lens, 1, and become nerve-end cells or retinula-cells, rt; in A, the letters rh point to a rhabdomere secreted by the cell rt; c, the peculiar central spherical cell; n, nerve fibres; mes, mesoblastic skeletal tissue; ch, chitinous cuticle.
The male possesses elaborate copulatory structures of a chitinous nature, and the eggs are fertilized in the female without even quitting the place where they are formed on the wall of the reticular gonocoel.
A 2 to a 5, Posterior borders of the chitinous bases of the coxae of the second, third, fourth and fifth prosomatic limbs.
That any partial fusion of originally distinct chitinous plates takes place in the cephalic shield of Trilobites, comparable to the partial fusion of bony pieces by suture in Vertebrata, is a suggestion contrary to fact.
This telson may enlarge, it may possibly even become internally and sternally developed as partially separate somites, and the tergum may remain without trace of somite formation, or, as appears to be the case in Limulus, the telson gives rise to a few well-marked somites (mesosoma and two others) and then enlarges without further trace of segmentation, whilst the chitinous integument which develops in increasing thickness on the terga as growth advances welds together the unsegmented telson and the somites in front of it, which were previ ously marked by separate tergal thickenings.
It must always be remembered that we are liable (especially in the case of fossilized integuments) to attach an unwarranted interpretation to the mere discontinuity or continuity of the thickened plates of chitinous cuticle on the back of an Arthropod.
Concentration of the organ-systems by fusion of neighbouring regions (prosoma, mesosoma, metasoma), pre viously distinct, has frequently occurred, together with obliteration of the muscular and chitinous structures indicative of distinct somites.
(X7.) D, E, Two views of the chitinous framework of a sucker of Axine belones; highly magnified (after.
Reproduction sexual and by means of "statoblasts," peculiar internal buds protected by a chitinous shell.
In many calcareous forms, .both Cheilostomes and Cyclostomes, the zoarium is rendered flexible by the interposition of chitinous joints at intervals.
In a few Gymnolaemata the ectocyst is merely chitinous, although in most cases the four vertical walls and the basal wall of the zooecium are calcareous.
The avicularium can move as a whole by means of special muscles, and its chitinous lower jaw m- ect.
Ann, Chitinous annulus, containing air cavities which enable the stato blast to float.
In the vibraculum the part representing the zooecium is relatively smaller, and the mandible has become the "seta," an elongated chitinous lash which projects far beyond the zooecial portion of the structure.
The tip of the proboscis is armed with a complicated series of chitinous teeth and rasps, by means of which the fly is enabled to pierce the skin of its victim; as usual in Diptera the organ is closed on the upper side by the labrum, or upper lip, and contains the hypopharynx or common outlet of the paired salivary glands, which are situated in the abdomen.
Ehrenberg), a genus of lobose Rhizopoda, characterized by a chitinous plano-convex shell, the circular aperture central on the fiat ventral face, and more than one nucleus and contractile vacuole.
In the shell of Lamellibranchs three distinct layers can be distinguished: an external chitinous, non-calcified layer, the periostracum; a middle layer composed of calcareous prisms perpendicular to the surface, the prismatic layer; and an internal layer composed of laminae parallel to the surface, the nacreous layer.
Nevertheless the filament is a complete tube formed of chitinous substance and clothed externally by ciliated epithelium, internally by endothelium and lacunar tissue - a form of connective tissue - as shown in fig.
H, Chitinous lining of the plate.
S, Chitinous framework of the axis.
The chitinous substance ch is observed to be greatly thickened as compared with what it is in fig.
12, c) and a proventriculus or " gizzard," whose function is to strain the foodsubstances before they pass on into the tubular stomach, which has no chitinous lining.