368 SECTIONAL TRANSACTIONS .—I. 
In lower vertebrates its bilateral symmetry is related to the symmetrical 
character of somatic movement. The tendency to right-handedness in 
the human subject reveals a difference between the right and left sides of 
the brain in respect of participation in visual reaction—but only when 
vision is concerned with perceptual reactions. 
AFTERNOON. 
Prof. Joun Tait and Dr. W. J. McNaLty.—Some features of the physiology 
of the frog’s utricular macule (2.45). 
Two types of operation, each extralabyrinthine, have been used. Firstly, 
the nerve twig of supply to each utricular macula has been divided without 
damage to the nervous connections of any of the other receptors. Secondly, 
the nerves to all the labyrinthine receptors except the utricular maculz 
have been put out of commission. 
The first kind of operation produces little conspicuous disability. Not 
only can the frog crawl, leap and swim, but it retains its body-righting 
reaction as well. The main disabilities are incapacity to land properly 
after free fall from a height, absence of compensatory adjustments of the 
(blinded) animal to slow tilt of the substratum, and a fine head tremor that 
accompanies all movement. 
A frog subjected to the second type of operation shows grave disorder. 
During any attempted movement it is subject to distressing bodily pendula- 
tion of a massive kind. ‘The animal retains its compensatory reactions to 
slow tilt. By quick tilt, on the other hand, it is at once impelled to execute 
an active movement of an opposite kind, whereby its balance is more than 
ever imperilled. 
Analysis indicates that the utricular otoconia are not simple weights that 
slip in a downhill direction on tilt of the head, but that they resemble buoys 
in being heavier at one end than the other. By means of a model one may 
show how such a conception of their structure fits all the available facts. 
Prof. JoHN Ta1t.—Evolution of voice in vertebrates (3.15). 
In terrestrial vertebrates intercommunication by means of sound involves 
(on the productor side) the respiratory apparatus with its supply of air. 
We tend to think of the emitted vocal signals as being air-conveyed, but 
fishes use water as the medium of communication. So does a frog, whose 
croaking apparatus is designed more for under-water than for above-water 
transmission. ‘The croak of the frog, best studied with a hydrophone, 
involves no loss of its contained air. Its mouth-sacs are amplifiers. The 
nasal sacs situated on the front of the skull of a whale are presumably 
similar amplifiers for an animal signalling below water with a self-contained 
volume of air. 
It is suggested that in its early origin the air-bladder of fishes subserved 
vocal as much as respiratory requirements. It happens for physical reasons 
that an enclosed volume of air, thrown into vibration by any means, is an 
excellent mechanism for production of low-pitched sounds. Having 
gulped air, certain early fishes apparently ‘ experimented’ along these 
lines. Eventually a special pocket, the air-bladder, developed in close 
relation with the motor apparatus of respiration. This view is based on 
the frequency with which different kinds of fishes, e.g. Cypriniformes, 
Dipnoi, not to mention others, have a sound-producing air-bladder. 
Terrestrial vertebrates came of an aquatic stock possessed of a vocal 
air-bladder. 
