— 10 — 



In regarcl to the outer gills of Oniscus he says: „Dans le genre Cloporte le bord externe 

 de chaque lame s'arrondit en un lobe tres mince; ce lobe est aussi forme de deux feuillets, mais 

 l'externe est aussi mince que l'interne. Les canaux qui donnent passage au fluide nourricier affectent, 

 dans cette partie, une disposition rayonnante." 



Leydig ' announced, in 1 855, that he had confirmed Siebold'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 capiUaries in the lungs of vertebrates. 



N. Wagner^ in au article entitled Appareil circulatoire des Porcellione s, publi- 

 shed 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 reaUty a sort of pulmonary sac 

 or trachea, serving as organs supplementary to the gills. He refers to certain histological features. 

 The gills are filled Avith 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, pubUshed in 1878.^ This author essayed to make an investigation of the histolo- 

 gical structure of the gills of PorceUio armadiüoides. Füll 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 zoölogists, as noted above. 



In agreement with bis 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 gül 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 erwälinten kleinen schräg 

 liegenden mit Luft erfüllten Höhlungen und indem wir genauer die Fläche durchmustern, können 

 wir wahrnehmen, 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 Wirkhchkeit bestehen solche 

 blindsackige Enden nicht, da ja die Luft in der cuticiüaren Wand der Bkitrüume liegt.'- 



What appears to be an opening is in fact a depression or recess in whicli a leaf-like ex- 

 tension of the basal Joint lies. That air comes out at this place under pressure can be esplained 

 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 hmg-breathing warrantable. It is in fact questionable 

 whether the air in this Situation has anything to do with respiratiou. 



' MüLLEH's Archives, 1855. 



' Annales des Sciences naturelles, 1865. 



^ Über Amphipoda and Isopoda, Zeitschrift für wissensch. Zoologie, Band 3o, Supplement, 1878. 



