188 SUMMARY OF CURRENT RESEARCHES RELATING TO 
oxygen tension of blood passing through the wall of the air-bladder is 
less than that of air, owing to the using up of oxygen for respiratory- 
purposes. Hence the blood will absorb oxygen from the air-bladder, the 
percentage of nitrogen will be increased, and it too will be absorbed. 
Thus, on the diffusion theory, all the gas would disappear from the air- 
bladder, whereas it may even increase in quantity. Section of the sym- 
pathetic nerve-fibres to the walls of the air-bladder hastens the secretion 
of gas into the empty bladder ; section of the vagus branch stops it 
entirely. It is not probable that the “ retia mirabilia,” discs of finely 
divided vessels in the walls of the swim-bladder, are directly connected 
with the secretion of gas, since they are under the epithelial lining. The 
epithelium itself is often differentiated into gland-like structures, as 
described by Coggi. These may be real air-glands, but they have never 
been fully investigated. It seems probable that molecules of gas are 
liberated from some form of combination within the cells lining the air- 
bladder, and that the process is continually going on. Some diffusion 
outwards must be constantly occurring, and when a fish is asphyxiated it 
quickly uses up the oxygen in the air-bladder. 
If the gas be thus liberated from combination within the cells, 
Mr. Haldane concludes, we have in the animal kingdom a process 
analogous to the liberation of oxygen from the green parts of plants, and 
the fixation of free nitrogen by the parasitic* organisms in Leguminosae, 
and it would seem that life is not so essentially an oxidation process as 
is commonly supposed. 
Hornet’s Venom antagonistic to Viper’s.* — M. C, Phisalix has 
made a number of experiments which go to show that the venom of 
hornets acts as a vaccine against the venom of vipers. The immunising 
substance is not destroyed by being heated at 120° C. ; it is soluble in 
alcohol ; it is neither an albuminoid nor an alkaloid ; but its real nature 
remains obscure. 
Tunicata. 
South African Tunicata. | — Dr. C. Ph. Sluiter describes a collection 
of thirty-two Ascidiacea collected on Prof. M. Weber’s South African 
expedition. In his introduction he discusses the vexed question of the 
classification of Ascidiacea, and gives his reasons for following this 
arrangement : — 
A. Ascidiacea socialia (Clavelinidae). 
B. Ascidiacea merosomata (== Aplousobranchia Garstang excL 
Clavelinidae). 
C. Ascidiacea holosomata. 
I. Phlebobranchiata (= Phlebobranchia Lahille and Gar- 
stang excl. Clavelinidae). 
II. Stolidobranchiata ( = Stolidobranchia Lahille and Gar- 
stang). 
The collection of thirty-two species includes twenty-eight which are 
new. 
* Comptes Rendus, cxxv. (1897)*pp. 977-9. 
f Zool. Jahrb. (Abth. Syst.), xi. (1897) pp. 1-61 (7 pis.). 
