Vol. IX, No. 1.] Sponges of the Lake of Tiberias. 71 
[V.S.] 
to be fully expanded. I havé pointed out elsewhere,!' it is 
doubtful whether the pore-cells of Spongillidae can contract in 
such a way as to obliterate the aperture they contain. 
re-examination of old preparations and a careful com- 
parison between them and those recently made leads me to the 
conclusion that highly developed pore-cells actually exist in the 
dermal membrane of most Spongillidae but can only be detected 
in unusually well-preserved specimens. In serial sections it is 
difficult, if not impossible, to see them. Their arrangement 
differs in different species; in some they are grouped as in 
N. mappa; in others they are practically confined to the edge 
of the sponge; in others again they occupy more or less clearly 
defined areas on the surface, and in some they are probably 
scattered. In those species such as Spongilla cartert in which 
the inhalent apertures appear to be comparatively large in 
ordinary well-preserved material, they are probably protected 
in the living sponge by a delicate dermal network in which the 
meshes are outlined by pore-cells. 
atever the exact origin of the pore-cells of the Spongil- 
lidae may be, and this is a problem that calls for a careful 
embryological iieatibation: that would be foreign to my own 
inquiries, they appear to be highly differentiated as mature 
cells from the ordinary pinacocytes of the dermal anaes 
In Spongilla crassissima, apart from their ring-like form, t 
closely resemble the cells that line the orifices of the ciliated 
crescent-shaped cells of similar structure joined together at the 
tips to enclose the aperture between them. My mistake was 
due to a slight folding of the membrane in some of my prepara- 
tions whereby two cells were brought into unnatural relations 
with one another. 
2. BIOLOGY AND ee ae OF THE SPONGES OF THE 
LAKE oF TIBERIAS. 
From a biological point of view the sponges of the Lake of 
Tiberias fall into two groups in accordance with the precise 
of the Jordan as it traverses the lake. The former group may 
be conveniently known as the littoral sponges; the latter as the 
sponges of the Jordan channel. 
! Faun. Brit, Ind.—Freshwater Sponges, etc., p. 32 (1911). 
2 Ree. Ind. Mus., I, p. 271 (1907). 
