Defense Mechanisms of Sponges, I — Cheng et al. 
399 
TABLE 1 
Results of 23 Differential Counts of the Five Types of Free Cells Found in the 
Parenchyma of Terpios zeteki 
COUNT NO. 
COLLENCYTES 
ARCHAEOCYTES 
CHROMOCYTES 
THESOCYTES 
SCLEROBLASTS 
1 
68 
14 
12 
5 
1 
2 
64 
10 
18 
8 
0 
3 
68 
14 
8 
10 
0 
4 
52 
34 
8 
4 
2 
5 
58 
20 
14 
6 
2 
6 
62 
18 
12 
8 
0 
7 
64 
20 
6 
8 
2 
8 
58 
22 
12 
8 
0 
9 
56 
20 
10 
14 
0 
10 
58 
24 
10 
8 
0 
11 
54 
26 
16 
4 
0 
12 
58 
24 
14 
4 
0 
13 
54 
30 
4 
12 
0 
14 
52 
20 
22 
6 
0 
15 
56 
24 
14 
6 
0 
16 
52 
24 
22 
2 
0 
17 
52 
24 
18 
6 
0 
18 
52 
32 
10 
4 
2 
19 
50 
24 
8 
18 
0 
20 
58 
24 
14 
4 
0 
21 
66 
24 
6 
4 
0 
22 
58 
22 
12 
8 
0 
23 
60 
18 
16 
6 
0 
Total 
1330 
512 
286 
163 
9 
Mean ± S.D. 
57.83 ± 5.39 
22.26 ± 5.54 
12.43 ± 4.82 
7.09 ± 3.68 
0.39 ± 2.2 
phenomenon has been reported by Tuzet 
(1932) who described what she termed "stel- 
late cells’’ in Regiera elegans (Bwk.) and R. 
simulans (Johnston) with anastomosing pseu- 
dopods. It is uncertain whether Tuzet’s "stellate 
cells” are homologous with T. zeteki collencytes, 
as she reported the presence in the former of a 
granular nucleus containing a nucleolus. As we 
have noted, nuclei of T. zeteki collencytes are 
agranular and without visible nucleoli. Simi- 
larly, Wilson and Penney (1930), who exam- 
ined Microciona prolifera Verrill, and de 
Laubenfels (1932), who studied lotrochota 
birotulata Higgin, have reported that many of 
the mesenchymal (parenchymal) cells in these 
sponges are connected by fine protoplasmic 
processes. Specifically, Wilson and Penney 
stated: "The space not occupied by canals, 
flagellated chambers, and skeletal fibers is filled 
with a tissue here designated as mesenchyme. 
It consists of abundant cells of several kinds, 
very many of which are connected together by 
intercellular strands. . . .” This situation, al- 
though superficially similar, is definitely differ- 
ent from that found in T. zeteki. In this sponge, 
collencytes are connected only with other collen- 
cytes and have not been observed to fuse with 
any other type of cell. Van Weel (1949), in a 
study of the freshwater sponge Spongilla proli- 
fer ens Annand, has also reported syncytially 
arranged "indifferent cells” with faintly stained 
clear cytoplasm, and which may be without a 
nucleolus. His "indifferent cells” are believed 
to be comparable to our collencytes. It is pro- 
posed that the collencytes of T. zeteki represent 
the basic type of structural cell in situ and 
provide a firm network which, together with 
the spongin fibers and spicules, add stability to 
the integrity of the parenchyma. The "stellate 
cells” of Regiera spp., as described by Tuzet 
(1932), and the "indifferent cells” of S. proli- 
fer ens, as described by van Weel (1949), 
appear to serve the same function. It is noted, 
however, that not all of the collencytes of T. 
zeteki are fused. Independent collencytes also 
occur. It is also of interest to note that the 
