The alimentary tract consists of a straight tube running from the mouth to the anus without any convolutions; it is separable into three divisions: (I) a muscular oesophagus, which is often provided with cuticular teeth; (2) a cellular intestine; and (3) a short terminal rectum surrounded by muscular fibres.
Investigations carried out by Blackman, and by Brown and Escombe, have shown clearly that the view put forward by Boussingault, that such absorption of gases takes place through the cuticular covering of the younger parts of the plant, is erroneous and can no longer be supported.
Similarly, the small amount of cuticular and of epidermal protection, and of lignification in succulent halophytes may also be related to the same circumstance.
Sub-cuticular tissue of the f, One of the retractors of the trunk and that of the pro g, A lemniscus.
H, Epidermic cell-layer; mes, mesoblastic connective tissue; n, nerves; II, III, IV, V, depressions of the epidermis in each of which a cuticular lens will be formed.
1, Cuticular lens.
L, Cuticular or corneous lens.
The chief peculiarities that distinguish Trematodes from their free-living allies, the Turbellaria, are the development of adhering organs for attachment to the tissues of the host; the replacement of the primitively ciliated epidermis by a thick cuticular layer and deeply sunk cells to ensure protection against the solvent action of the host; and (in one large order) a prolonged and peculiar life-history.
(X 330: from Thomas.) attachment to the innermost cuticular layer by slender processes.
It is to be remembered that the whole of the cuticular hard product produced on the dorsal surface and on the mantle-flaps is to be regarded as the " shell," of which a median band-like area, the ligament, usually remains uncalcified, so as to result in the production of two valves united by the elastic ligament.
21), so that its fibres join the anterior faces of the nerve-end cells as in Vertebrates, instead of their posterior faces as in the cephalic eyes of Mollusca and Arthropoda; moreover, the lens is not a cuticular product but a cellular structure, which, again, is a feature of agreement with the Vertebrate FIG.
Rudimentary cephalic eyes occur in the Mytilidae and in Avicula at the base of the first filament of the inner gill, each consisting of a I pigmented epithelial fossa containing a cuticular lens.
The foot is a muscular mass without cuticle or skeleton, excepting certain cuticular structures such as the byssus of Lamellibranchs and the operculum of Gastropods, which do not aid in locomotion.
The alimentary tube consists of three regions: firstly, the anterior buccal mass with the oesophagus, of ectodermic origin, and therefore bearing cuticular structures, namely the jaws and radula; secondly, the mid-gut, of endodermic origin and including the stomach and liver; and, thirdly, the hind-gut or intestine.
Into these fins, which are largely cuticular and strengthened by radiating bars, a single layer of ectoderm cells projects.
H, Space in sub-cuticular layer of the skin.
As in all Arthropoda, it is composed of three divisions, a fore-gut or stomodaeum, ectodermal in origin and lined by an inturning of the chitinous cuticle, a mid-gut formed by endoderm and without a cuticular lining, and a hind-gut or proctodaeum, which, like the fore-gut, is ectodermal and is lined by cuticle.
Further, a definite cuticular membrane is frequently formed and shed at this stage, which corresponds to the nauplius-stage of larval development.
They are lined internally by a cuticular deposit of chitin.
The black represents the cuticular product of the epidermal cells of the ocular area, taking the form either of))...,r,, f lens, cl, of crystalline body, cry, or of rhabdom, rhab; hy, hypodermis or epidermal cells; corn', laterallyplaced cells in the simpler stage, A, which like the nerve-end cells, vit' and ret', are corneagens or lens-producing; corn, specialized corneagen or lens-producing cells; vie, potential vitrella cells with cry', potential crystalline body now indistinguishable from retinula cells and rhabdomeres; vit, vitrella cell with cry, its contained cuticular product, the crystalline cone or body; ret', rhab', retinula cells and rhabdom of scorpion undifferentiated from adjacent cells, vit'; ret, retinula cell; rhab, rhabdom; nf, optic nerve-fibres.