10 
In regard to the outer gills of Oniscus lie says : „Dans le genre Cloporte le bord externe 
de chaque lame s’arrondit en im lobe tres mince ; ce lobe est aussi forme de deux feuillets, mais 
I’externe est aussi mince que I’interne. Les canaux qui donnent passage au fluide nourricier affectent, 
dans cette partie, une disposition rayonnante.“ 
Leydig' announced, in 1855, that be bad confirmed Siebold’s conclusion that the corpora 
alba contain 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. Wagner^ in an article entitled Ap2iareil circiilatoire des Porcelliones, publi- 
shed in 1865, stated that the outer lames, taken together, form a kind of respiratory chamber, 
bolding 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 Leydig, published in 1878.® This author essayed to make an investigation of the histolo- 
gical 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) Leydig 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 Hohlen der Cuticula enthalten, daher die ‘feine Zerteilung‘ . . . 
Man sieht bier innerhalb der feldrigen Abgrenzungen die vorhin schon erwahnten kleinen schrag 
liegenden mit Luft erfiillten Hohlungen und indem wir genauer die Flache durchmustern, konnen 
wir wahrnehmen, dass sie wohl auch in gewohnliche Porenkanale ubergehen, 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 Blutraume liegt.“ 
What apjiears to be an opening is in fact a depression or recess in which a leaf-like ex- 
tension of the basal joint lies. That air comes out at this jdace 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 physio- 
logical 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. 
' MtiXLBE’s Archives, 1856. 
Annales des Sciences naturelles, 1865. 
^ fiber Amphipoda and Isopoda, Zeitschrift fiir wissensch, Zoologie, Band 30, Supplement, 1878. 
