SPONGIIDA. 
12 Spong. 
to be dissimilar from those of all other groups. Balfour thinks it might 
be possible to regard Sponges as degraded from Actinozoa, such as Alcy- 
onium, but prefers, in default of sufficient evidence, to consider them as 
an independent group of the Metazoa. 
VosMAER, (15) enumerates four main types of canal system in Sponges, 
viz., 1. Ascon, with collar-cell area opening directly to exterior. 2. Sycorif 
with collar-cell area opening to gastral cavity. 3. Represented by Aply- 
silluj Spongelia, Halisarca dujardiniy Leucandra aspera^ most Renierida^ 
some Suheritida, and probably the Hexactinellida ; the collar-cell areas 
open into wide canals, which open directly or by larger canals. 4. Repre- 
sented by Aphysina, Ruspongia, Cacospongia, Hircinia, Oligoceras, Pla- 
cortisy Plannastrella ; with Halisarca lohulariSy Chondrosia, Chondrilla, 
Corticium candelabrum ^ showing a higher grade. The collar-cell areas 
lead into usually fine canals, which end ultimately by way of two (second- 
ary and primary) degrees of canals, in the gastral chamber. Vide supra, 
Calcarea, for special application of views to that group. 
Kerasine. Term applied by Carter to the horny material contained 
in the fibres of many Sponges, (4). 
The horny fibres, according to Carter, 1. c., in some cases contain 
cells, but are all formed round a central granular core. 
Keratose, (13) p. 480, distinguished by Ridley, by means of its power 
of polarizing light, from a similar substance, also occurring in Sponges, 
to be termed pseudo-keratose. 
Elastic tissue said by Carter, (5) p. 255, to be found in Carnosa and 
in many other Sponges. 
Pigment-cells in Luffaria and Aplysina, lanthella, Spongia, Stelletta, 
DercituSy Chondrillay Dysidea, described by Carter, (4) p. 105, pi. ix. 
figs. 3-9 ; they may either be globular or elliptical, or stellate, or com- 
posed of irregular aggregations of granules. 
Carter, (4) states that the ornamental parts of a Sponge-spicule are 
added after the rest of the spicule has been formed. 
Tibiella. Term applied by Carter, (2) p. 3G9, to the “ biclavated 
cylindrical ” spicule of Bowerbank. 
Spongia cartilaginea, Esper. Specimens of what he considers to be 
this species, described and figured by K. Semper in The Natural Con- 
ditions of Existence as they affect Animal Life : London, 1881, 8vo 
(Internal. Scient. Series), p. 343, figs. 92 & 93, as showing commingling 
of sponge-tissues with those of algae. 
Heteromorphic zooids in Sponges. The two kinds of processes de- 
scribed by him on the surface of Alemo seychellensis, E. P. Wright, 
g. & sp. nn. (16) p. 15 (see above), are thus described by that author ; 
in a note added subsequently, p. 17, he compares this phenomenon with 
the budding exhibited by Tethya and Rinalda, as being possibly of the 
same nature. 
A large number of different forms of enlargement of the axial canal 
in siliceous Sponge-spicules are described and figured by Duncan, (6) ; 
the most common is a symmetrical tear- (or pear-) shaped cavity, which may 
be repeated several times in the same spicule ; the cavity usually appears 
to be closed to the exterior. However, cases 03cur iu which the axial 
