6 Spong. 
XVII. SPONGL/E. 
the fibres composed of an axial pith and a superficial cortex. There is no 
strict boundary between these, the former passes gradually into the latter. 
The pith appears granular, the granules being situated in longitudinal 
rows. Both pith and cortex are spirally striated. There are two spiral 
striations crossing each other. Desiccation and examination with high 
powers reveal a “ Wabenstruktur ” in the fibres, the whole substance of 
which contains small cavities lying in longitudinal and spiral lines. 
d. Epithelia, Cuticula [cf. Titles 8, 33]. 
Delage & Herouard (8) think that, at least in some sponges, a 
“ Sollas-membrane ” connecting the collar-margins of the collar-cells is 
present. They do not believe in the existence of distal processes arising 
from the base of the collar-cell. 
Schulze (33) publishes the results of his histological examination of 
Schaudinnia arctica , a Bosselid Hexactinellid discovered by Sc-haudinn 
(vide 32). This material was very carefully preserved. The collar-cells 
cover, as a continuous epithelium, the whole chamber-wall. The upper 
ends of the bodies of adjacent collar-cells are attached to each other. The 
flattened nucleus lies basally. At the base the collar-cell is considerably 
extended and here it gives off granular processes which connect the basal 
parts of adjacent cells. Four of the processes of each cell, situated like 
the arms of a cross, are much stouter than the others. In adjacent collar- 
cells these extend in nearly the same direction and coalescing form a 
network with quadratic meshes. The collar shows no visible structure. 
There is no basal membrane in the chamber-wall. The superficial cells 
covering the trabeculae which traverse the incurrent cavities are stout, 
protrude from the surface and contain bulbous bodies. Their nuclei are 
small and spherical, whilst the nuclei of the cells in the deeper layers are 
large and oval. The smallest trabeculae appear to be destitute of the 
micro-nuclear epithelium: here the macro-nuclear cells reach the surface. 
e. Sexual Cells, Propagation and Development [cf. Titles 
10, 25, 44, 45, 47]. 
Evans (10) has examined the free-swimming larva and young fixed 
individuals of Spongilla. The youngest larva studied is oval and consists 
of a single, continuous, superficial layer of elongated flagellate cells on the 
surface and two kinds of cells, such with granular and such with vesicular 
nucleus in the interior. Later on small cells arranged in groups are 
produced in the interior and the flagellate superficial cells dive down into 
the inner mass of cells. These flagellate cells and also the small group- 
cells are converted into collar-cells. During this conversion the flagellate 
cells join for a time the vesiculo-nuclear cells of the interior, which are 
rich in yolk-granules and form with them plasmodial masses from which 
those groups of collar-cells which constitute the ciliated chambers are 
afterwards segregated. In some larvae only few group-cells are formed; 
in these nearly the whole of the collar-cells are derived from the— 
originally superficial—flagellate cells. In others the group-cells become 
numerous and in these a considerable number of the collar-cells of the 
adult are transformed group-cells. Evans tries to explain the differences 
of the statements of previous observers concerning the origin of the collar- 
cells in Spongilla with these differences of different larvae examined by 
himself. The outer epithelium of the sponge is derived from the granulo- 
nucleated cells of the interior. The excurrent canals are formed in situ 
and do not grow out from the original larval cavity which in most cases 
completely disappears. 
