| Amphioxi
(adj. amphioxous) | Rod-like spicules
sharp at both ends. |
| Amphistrongyli (adj.
amphistrongylous) | Rod-like
spicules blunt at both ends. |
| Basal
membrane | A horny, structureless
membrane found at the base of some sponges. |
| Birotulate (subst. or
adj.) | Spicule with a transverse disk at
both ends. |
| Bubble-cells | Spherical cells of the parenchyma the contents of which
consist of a drop of liquid covered by a thin film of
protoplasm. |
| Ciliated
(or flagellated) chamber | A
cavity lined with collar-cells. |
| Collar-cell
(choanocyte) | Cell provided at one
end with a membranous collar and a vibratile lash or flagellum that
springs from within the collar. |
| Derma or
ectodermal layer | A layer of flat
cells arranged like a pavement on the surface of the sponge. |
| Exhalent
(or efferent) canal | A
tubular canal through which water passes from a ciliated chamber towards
the osculum. |
| Fibres
(skeleton) | Thread-like structures that
compose the skeleton of the sponge and are formed (in the Spongillidæ)
mainly of overlapping spicules. |
| Flesh-spicules | Microscleres (q. v.) that lie free in the
parenchyma and the derma. |
| Foramen | An orifice
of the gemmule. |
| Foraminal tubule | A
horny tube that surrounds the foramina of some gemmules. |
| Gemmule | A mass of
cells packed with food-material, surrounded by at least one horny coat,
capable of retaining vitality in unfavourable conditions and finally of
giving origin to a new sponge. |
| Green corpuscles | Minute green bodies found inside cells of sponges and
other animals and representing a stage in the life-history of an alga
(Chlorella). |
| Inhalent (or afferent)
canal. | A tubular canal through which water passes
from the exterior towards a ciliated chamber. |
| Megascleres | The
larger spicules that (in the Spongillidæ) form the basis of the skeleton
of the sponge. |
| Microscleres | Smaller spicules that lie free in the substance or the
derma of the sponge, or are associated with the gemmule. |
| Monaxon | (Of
spicules) having a single main axis; (of sponges) possessing skeleton
spicules of this type. |
| Osculum | An aperture
through which water is ejected from the sponge. |
| Oscular collar | A
ring-shaped membrane formed by an extension of the derma round an
osculum. |
| Parenchyma | The
gelatinous part of the sponge. |
| Pavement layer | Adherent gemmules arranged close together in a single
layer at the base of a sponge. |
| Pneumatic coat | A
horny or chitinous layer on the surface of the gemmule containing
air-spaces. If these spaces are of regular form and arrangement it is
said to be cellular; if they are minute and irregular it is
called granular. |
| Pore | A minute hole
through which water is taken into the sponge. |
| Pore-cell (porocyte) | A cell pierced by a pore. |
| Radiating fibres | Fibres in the skeleton of a sponge that are vertical or
radiate from its centre. |
| Rotula | A transverse
disk borne by a microsclere. |
| Rotulate (subst. or adj.) | Spicule bearing one or two transverse disks. |
| Spicule | A minute
mineral body of regular and definite shape due not to the forces of
crystallization but to the activity of the living cell or cells in which
it is formed. |
| Spongin | The horny
substance found in the skeletal framework and the coverings of gemmules
of sponges. Structures formed of this substance are often referred to as
chitinous. |
| Subdermal cavity | A
cavity immediately below the derma (q. v.). |
| Transverse fibres | Fibres in the skeleton of a sponge that run across
between the radiating fibres. |
| Tubelliform (of
spicule) | Having a straight shaft with a
transverse disk at one end and a comparatively small knob-like
projection at the other. |