SPONQIJK. 
14 tipong. 
cavity. Vosmaeria corticata (pp. 298 & 299) has a peculiar canal system, 
resembling greatly that of Hexactinellida. For the canal system of Cal- 
carea in general, see pp. 370-382. Epithelium of Calcar ea { p.394). In 
Asconidce, Leucopsulcc, and Leuconulcc,. the entire flattened epithelium, in 
all the canals as well as on the outer surface, is of ectodermal nature, 
while the endoderm is represented by the collar cells in the Ascon tubes, 
and in the chambers of Leucopsidce aud Leuconidic. In Ilomodermidcv, 
Syconidce , and Sylleibidce , the external surface and the inhalant canals are 
clothed by ectoderm, the chambers, excurrent canals, and oscular tube 
with endoderm. The collar cells (p. 396) are connected by processes 
with one another, or send out fine threads which anastomose between the 
cells. In Ascetta primordial is (pp. 200 & 201) the collar cells do uot 
touch one another, but are separated by clear spaces containing an inter- 
vening substance similar to the ground substance of the mesoderm. This 
intervening substance forms a network of trabecuke of varying thick- 
ness. The larger trabeculae contain an axial protoplasmic thread. In 
the nodes of the network these threads anastomose and usually form at 
these points distinct thickenings. Between the collar cells are often 
multipolar protoplasmic masses, containing one or more nuclei, according 
to size. All transitions occur from the largest multinuclear structures of 
this kind to the small thickenings of the protoplasmic threads at the 
nodes of the intercellular network. Sometimes two collar cells are con- 
nected with one another by a broad bridge of protoplasm. More often 
they send off fine threads, which can be followed to some distance. 
Most collar cells, and all the multipolar elements, whether largo and 
multinuclear or small and nonnucleated, are united with this network of 
threads, which is probably the result of multiplication of the collar cells 
by division. The large nucleated multipolar cells are to be looked upon 
as “ mother collar cells ” (Kragenmutterzellen). They occur only in 
growing parts of the Sponge, producing collar cells which multiply further 
by division. The small non-nucleated lumps of protoplasm at the nodes 
of the network of threads are the final indifferent remains of the 
“ mother collar cells.” A collar cell layer of similar structure occurs in 
Ascetta spinosa (p. 205), A. cerebrum (208), A. clathrus (211), A. blanca 
(p. 218), A. gcethei (p. 221), Ascandra reticulum (p. 224), A. angulata 
(p.227), Ilomandra falcuta (p. 231), and Vosmaeria corticata (p. 299). 
In Sycandra raphanus (pp. 253 & 254) the collar cells are separated by 
intervening substances, but multipolar masses of protoplasm between the 
cells were not to be found. The collar cells send down processes into 
the mesoderm. Near the edge of the osculum occur pear-shaped cells, 
usually united in groups, with their thick ends in contact. The other 
end runs out into a long process. These groups of cells are the rudi- 
ments of flagellated chambers, and the pear-shaped cells become trans- 
formed into collar cells. The collar cell layer is similar in Sycandra 
tuba (p. 245), S. setosa (p. 259), and Amphoriscus cylindrus (p. 286). In 
Ascetta spinosa (p. 205), granular, brownish cells occur in the collar cell 
layer, which are probably parasites of symbiotic vegetable organisms. 
