146 
performs the office of a stomach, the 
external surface probably acts as an 
organ of respiration. Many of the 
vermes appear, in like manner, to 
have an external respiration: this is the 
case with the leech and the earth- 
worm, in which a superficial net-work 
of vessels receives the influence of the 
Surrounding fluid. In some genera of 
this class, it was stated, this structure 
is confined to particular parts of the 
surface; and in others, again, the res- 
piratory organs shoot out from the body 
in the form of bushy fibrils. The dif- 
ferent situations of these arborescent 
gills, which are frequently kept in in- 
cessant motion, were pointed out in 
several orders of molluscous and 
crustaccous animals. 
Dr. Roget then proceeded to exa- 
mine the extensive series of animals 
in whom respiration takes place in the 
interior of the body: beginning with 
the holothuria, the ramified tubes of 
which exhibit the first trace of a struc- 
ture adapted to this object; the asteria, 
and the echinus, in which the arrange- 
ment is somewhat more complicated ; 
and the larger crustacea, as the lobster 
and crab, in which the filaments are 
collected into a number of pyramidal 
organs on each side of the body, pro- 
tected by the shell, and terminating 
with the more regular structure of 
gills proper to the ordinary mollusca, 
and fishes, The disposition of these 
organs, with reference to the shell, and 
to the apertures in the mantle, by which 
the water is admitted to them ; and the 
provision of tubes, capable of being 
extended and retracted, in those shell- 
fish that burrow in the sand; were se- 
verally pointed out and described. 
The two auxiliary hearts of the cuttle- 
fish, at the origin of the bronchial 
arteries, by which the blood of that ani- 
mal is propelled with force to the 
respiratory organs, while the principal 
heart carries on ‘the aortic or greater 
circulation, were particularly noticed. 
‘~The importance of the respiratory 
functions increases as we rise in the 
Scale of animals. In fishes, the gills 
form a considerable portion of the sys- 
lem, and their office appears to be 
more essential to life than in the 
mollusca. The situation and structure 
of these organs’ were minutely de- 
scribed, torether with the mechanism 
by which their action is maintained. 
The air contained in ‘the water is 
equally vitiated by the respiration of 
fishes, and requires an cqually con- 
Proceedings of Public Societies. 
[s ept. 1; 
stant renewal as in ‘terrestrial ani- 
mals. Fishes are, therefore, killed in 
a short time, if confined in a limited 
portion of water which has noaccess to 
fresh air. When many fish are inclosed 
in anarrow vessel, they all struggle for 
the uppermost place, where the at- 
mospheric air is first absorbed, like the 
unfortunate men imprisoned in the 
black hole at Calcutta. In Humboldt 
and Provengal’s experiments, a tench 
was found to be able to breathe when 
the quantity of oxygen in the water 
was reduced to the five-thousandth 
part of its bulk, though it is in this 
way brought into a state of extreme 
debility: but the fact itself shows the 
great perfection of the organs in this 
fish, that can extract so minute a 
quantity of air from water, to which 
the last portions always adhere with 
great tenacity. 
The respiration of air in its gazeous 
state is performed by breathing terres- 
trial animals in two ways: first, by 
means of trachez, a mode peculiar to 
insects; and, secondly, by pulmonary 
cavities, which constitute the essential 
structure of lungs. The trachee of 
insects are tubes which take their rise 
by open orifices, called spiracles or 
stigmata, from the surface of the body, 
and are distributed by extensive 
ramifications to every part. They ex- 
tend even to the wings, to the sudden 
expansion of which they appear to 
contribute. In the higher classes of 
articulated animals, as soon as blood- 
vessels are met with, the whole ap- 
paratus of trachez is found to disap- 
pear ; their necessity being superseded 
by the power, derived from the pos- 
session of circulating vessels, of trans- 
mitting the juices to particular organs, 
where their exposure to the influence 
of the air may be conveniently ef- 
fected. ‘The pulmonary cavities of 
spiders, and of some gasteropodous 
mollusca, such as the snail and slug, 
which breathe atmospheric air, are of 
this description. 
The structure of the pulmonary or- 
gans becomes more refined and com- 
plex as’ we proceed to the higher 
classes of animals. Dr. Roget entcred 
into a description of these various 
structures, and of the diversified 
modes in which the air was received, 
and made to act upon them, and after- 
wards expelled, in the different orders 
of reptiles, of mammalia, and of birds. 
The singular mode in which the frog 
swallows its air, and inflates its lungs 
at 
