564 PROF. HUXLEY ON THE RESPIRATORY [June 20, 
tions, which are in relation with the pulmonary parenchyma, are per- 
forated by minute rounded apertures. These lead into canals which 
are directed, at first, more or less at right angles to the surfaces of the 
bronchia upon which they open, and pass, side by side, sometimes 
anastomosing with one another, to some other bronchium than that 
from which they start. They may be termed parabronchia (“canaux 
tertiaires,” Cuvier; “bronchial tubes,’ Rainey; “ Lungenpfeifen” of 
the Germans). The lumina of these canals are interrupted at pretty 
regular intervals by transverse circular folds which contain unstriped 
muscular fibres. The interspaces between these folds are more or 
less subdivided by oblique or longitudinal folds of a similar nature 
into fosse ; and the walls of these fossee present smaller depressions 
or fessule, which directly, or indirectly, open into the intercapillary 
air-passages. These last occupy the meshes of the capillary network 
into which the pulmonary vessels resolve themselves. 
This description (with possibly some variation in the number of 
the ostia and air-sacs) applies to the respiratory apparatus of every 
known bird, and to that of no other animal; but it also applies, almost 
word for word, to Apterya. Hence there can be no doubt that the 
respiratory organs of this bird are thoroughly and typically ornithie, 
and that they present not the slightest approximation to those of the 
Mammalia. 
If the organs of respiration of Apterya are compared with those 
of a carinate bird of similar size and form of trunk, such as a Duck, 
the resemblances and differences between the two can be easily 
traced. 
1. The Duck’s lungs are considerably larger both absolutely and 
relatively. 
2. The anterior ventral margin in the Duck is longer than the 
posterior. The reverse obtains in Aptery2. 
3. The pulmonary aponeurosis of the Duck is very delicate; in 
Apteryz it is strong and thick. 
4, The median vertical septum in the Duck is much deeper, and 
anteriorly it is supported by the long hypapophyses of the anterior 
thoracic vertebree. At the same time it is far less strongly fibrous 
than the corresponding structure in Apteryx. The mesial attachment 
of the pulmonary aponeurosis is to the ventral edge of the septum, 
close to that of the oblique septum, in the Duck ; while in Apteryx 
the two are separated by a considerable interval, throughout which 
the thin andmembranous part of the dorsal median septum divides 
the mesial ends of the intermediate and posterior loculi from one 
another. 
In the Duck, the median dorsal septum lies throughout between 
the superior facets of the internal faces of the two lungs. In other 
words, this superior facet is much deeper in the Duck than in 
Apteryx. 
5. The oblique septum is extremely thin and weak in the Duck ; 
while in Apteryx it is a very strong aponeurotic membrane, with 
interlacing fibres diverging from two tendons attached to the under 
face of the posterior thoracic vertebree. In the Duck it contains, on 
