PaJatabiJity of Marine Invertebrates — Russell 
457 
TABLE 2 ( Continued ) 
MATERIAL TESTED 
NO. OF 
trials 
PART OF 
ANIMAL 
USED 
Gambusia 
Carassius 
delates 
Torquigener 
Catostylus mosaicus 
2 
homogenate 
of whole 
0 
0 
0 
0 
Cert ant bus sp. 
3 
base 
0 
0 
0 
0 
3 
tentacles 
of live 
animal 
0 
0 
0 
0 
2 
tentacles 
of dead 
animal 
0 
0 
0 
0 
Other anemone 
1 
tentacles 
of dead 
animal 
0 
0 
0 
0 
ENTEROPNEUSTA 
Glossobalanus sp. 
4 
anterior 
part of 
body 
0 
0 
0 
0 
PISCES 
Sillago maculata 
Quoy & Gaimard 
2 
muscle 
0 
0 
0 
0 
Torquigener hamiltoni 
(Gray & Richardson) 
3 
muscle 
0 
0 
0 
0 
In the preparation of gelatin-base mixtures, a 
mixed homogenate of Metapenaeus and of test 
tissue was combined with an equal weight of 
40% gelatin in sea water to give a final con- 
centration of 20% gelatin. Metapenaeus + test 
tissue mixtures were made in the following 
proportions : 
METAPENAEUS 
TEST TISSUE 
FINAL CONC. 
OF TEST 
TISSUE (%) 
5 parts 
0 parts 
0 
4 parts 
1 part 
10 
3 parts 
2 parts 
20 
2 parts 
3 parts 
30 
1 part 
4 parts 
40 
0 parts 
5 parts 
50 
(A criticism of this method is that the concen- 
tration of Metapenaeus alters as well as that 
of the test tissue. But if the Metapenaeus con- 
centration is kept constant, the total concentra- 
tion of tissue, and therefore of texture, is al- 
tered. ) 
Within each series, tests were made to find 
the concentration of test tissue required to make 
the whole unpalatable. This was checked by 
comparison with the concentrations above and 
below. Tests of different parts or secretions of 
some animals were also made in this way. 
Results 
Table 4 lists the animals tested and the 
concentration necessary to make the mixture 
of prawn and gelatin unpalatable. Materials 
are arranged in three groups; the difference 
between the two "slightly unpalatable’’ animals 
and the others is probably real, but the signifi- 
cance of the difference in effect between con- 
centrations of 20% and 30% of test tissue 
could be questioned. 
In no case was there any noticeable difference 
in palatability between different parts of an ani- 
mal. When the fresh purple ink of the opis- 
thobranchs No tare bus and Dolabella was intro- 
duced into the fish tanks, the fish swam towards 
it and through it, often biting at local higher 
concentrations. 
EXPERIMENT IV 
SURFACE pH 
Thompson and Slinn (1959) and Thompson 
(1960a, b) have shown that some molluscs 
produce a defensive acid external secretion 
