In regard to the outer gills of Oniscus he says: „Dans le genre Cloporte le bord externe
de chaque lame s’arrondit en un lobe très mince; ce lobe est aussi formé de deux feuillets, mais
l’exteme est aussi mince que l’interne. Les canaux qui donnent passage au fluide nourricier affectent,
dans cette partie, une disposition rayonnante.“
L e y d i g 1 announced, in 1855, that he had confirmed S i e b o l d ’s conclusion that the corpora
alba coutain very finely divided air. He stated that the air passages form a finely-meshed network,
similar to the capillaries in the lungs of vertebrates.
N . W a g n e r a in an article entitled A p p a r e il c ir c u la to ir e des P o r c e llio n e s , published
in 1865, stated that the outer lames, taken together, form a kind of respiratory chamber,
holding moist air which is indispensable for the inner gills. The corpora alba resemble very much
the respiratory organs of the arachnids and insects. They are in reality a sort of pulmonary sac
or trachea, serving as organs supplementary to the gills. He refers to certain histological features.
The gills are filled with a spongy tissue “tissu spongieux“. The walls are composed of two layers,
the inner of which consists of “celles sous-epidermiques“. Within the gills, mainly aggregated in
one place, are the “gouttelettes de la graisse“.
The last work that has appeared relating to the breathing-organs of the land-isopods is
that of L e y d i g , published in 1878.8 This author essayed to make an investigation of thé histological
structure of the gills of Porcellio armadilloides. Full comment upon this work is given in the
body of the present treatise. It will be to our purposo to notice here the conclusions which he
reached in regard to the main points previously investigated by zoologists, as noted above.
In agreement with his previous determination (see above) L e y d i g finds that the corpora
alba contain finely divided air. But this air does not enter or pass out, as had been reported by
others and as he himself had formerly believed, through an opening on the posterior margin of
the gill-cover. Scattered over the entire surface of the gill are small pneumatic spaces of the
cuticle. “Die Luft ist in kleinen Höhlen der Cuticula enthalten, daher die ‘feine Zerteilung* . . .
Man sieht hier innerhalb der feldrigen Abgrenzungen die vorhin schon erwähnten kleinen schräg
liegenden mit Luft erfüllten Höhlungen und indem wir genauer die Fläche durchmustern, können
wir wahmehmen, dass sie wohl auch in gewöhnliche Porenkanäle übergehen, somit nur eine besondere
Form der letzteren darstellen.“
Previous authors were in error in their estimation that the air-holding part was a branching
divided sack with blind closed ends, after the form of a glaud. “In Wirklichkeit bestehen solche
blindsackige Enden nicht, da ja die Luft in der cuticularen Wand der Bluträume liegt.“
What appears to be an opening is in fact a depression or recess in which a leaf-like extension
of the basal joint lies. That air comes out at this place under pressure can be explained
by supposing that the bottom of the depression in thinner there than the skin elsewhere is.
Concerning the significance of the organisation described, the author states that it is not
to be regarded as morphologically corresponding with the tracheae of insects, nor, on the physiological
side, is the conception of a kind of lung-breathing warrantable. It is in fact questionable
whether the air in this situation has anything to do with respiration.
1 MüiiiiEB’s ArcMves, 1855.
2 A nna le s de s S ciences n a tn re lle s , 1865.
8 Ü b e r Am phipoda a n d Iso p o d a , Z e its c h rift fü r wissensch. Zoologie, Ban d 30, S u pplement, 1878.
It is seen from the above review of the literature that, although the organs of respiration
of the Oniscidae have been the subject of investigation by a considerable number of zoologists,
scarcely anything concerning their more intimate characters can be said to have been finally settled.
Leaving out of account the aberrant views of T r e v i r a n u s and B r a n d t , the only point as to
which there had been some approach to unanimity of opinion was that the corpora alba are organs
containing air. Even as to this D u v e r n o y and, at the time of the publication of their joint work,
his collaborator, L e r e b o u l l e t , were at least in doubt. They record that they observed a clear
liquid to pass out from the aperture associated with the corpora alba, and their final conclusion
was that the organ served to abstract the moisture from the air.
As to the precise structure of the same organ, the statements of the several authors are
widely divergent. In its general features it has been compared variously to a tree, a sponge and
a net-work. As to its physiological nature it has been regarded at times' as a form of trachea,
again as a lung, and again as a modified gill.
The only histological investigation made has been that of L e y d i g and the conclusions
reached by him, in regard to the corpora alba, were contradictory, in respect to nearly all essential
points, to those reached by his predecessors. Moreover, a reading of L e y d i g ’s article shows that
as an histological study it is incomplete.
The investigations hitherto made upon the special modifications of the outer divisions of
the respiratory appendages have been confined to the genera Porcellio and Armadillidium. It has
not been hitherto discovered that also in the genus Oniscus there are highly specialized structures,
though quite different in their morphological characters, adapted to the performance of the respiratory
function in air.
It is evident that a thorough investigation, employing the resources of modem laboratory
methods, was to be desired in order to add to our knowledge of these interesting organs. The
writer believes that the work here submitted is a contribution to that end.
M IE K /