229 
who kindly assented to my occupation of the University College table 
for four weeks at the Plymouth Station and to the staff of the Station 
for the great assistance they afforded me in connection with my work. 
The Artificial Activation of the Gas Gland. 
My first objects were to find suitable teleosts, i. e. teleosts in 
possession of large well-defined gas glands and retia mirabilia, for the 
experiments and to cause the gas glands to become active. The 
fish I worked with were principally Pollack (Gadus pollachius), 
Conger (Conger vulgaris), Mullet (Mugil chelo), Wrasse (Labrus 
maculatus, Ctenolabrus rupestris) and Siphonostoma typhle. I 
found Pollack to be most suitable, chiefly on account of the plentiful 
supply (I used about 60), their size, their habit of swimming 
off the bottom and their tough constitution (handling not affecting 
them). The chief method I employed in order to “activate” the 
gland was to attach a small lead weight ventrally by means of a 
thin silvered wire looped round the body just behind the pectorals 
and the pelvics and tied dorsally just in front of the anterior dorsal 
fin. The loop of wire was only tied sufficiently tightly to avoid 
slipping and in no way interfered with the movements, vigor or general 
comfort of the fish. I adopted this method because I had already 
proved its efficacy on Perch (15) and I was debarred from using a 
trocar. Roughly speaking, the weight attached was 5 °/, of the 
weight of the fish. I give some examples of the actual weights 
employed: 
The Pollack weighed 195 grams, the weight attached weighed 11 grams 
” ” ” 1 30 ” ” ” 7 n Z ”» 
” ” ” 85 ” 9 ” ” ” ) ” 
” ” ” 125 ” 7 ” ” 7 5 ” 
” ” ” 87 ” ”? ” ” ” 5 ” 
? ” ” 68 ” ” ” ” ” 3 Ph 
” ” ” 100 ” I ” ” ” 5 
When the weight is first attached, the fish nearly always immediately 
sinks to the bottom where it usually rests for a few minutes. Soon 
however it swims upwards and adopts the position shown in text- 
figure 2 B, the inclined position being maintained by the swimming 
movements of the tail. The fish, in fact, is swimming upwards the 
whole time in order to counteract the sinking tendency of the weight. 
The reason why the fish, thus weighted, persists in swimming instead 
of resting on the bottom (a sign that the experiment is not proceeding 
satisfactorily) is doubtless due to the special necessity of aerating 
