540 
DE. A. GUNTHER’S DESCRIPTION OE CERATODUS. 
runs in an oblique direction from the front end of the pseudobranchia inwards ; the 
other (A 1 ) remained attached to the cerato-hyal (c h): The pseudobranchia of Ceratodus 
corresponds evidently to the opercular gill of Lepidosiren and Protopterus ; but it cannot 
have the same function, inasmuch as in these two genera a separate portion of the first 
arcus aortse branches off to carry (venous) blood to this gill, thus proving its function to 
be respiratory (Kiemendeckel-Kieme of Muller), whilst in Ceratodus the first arcus 
aortse has no branch for the pseudobranchia before it enters the foremost real gill. 
Spiracles are absent. 
Thus we can add another combination with regard to the coexistence of opercular 
gill, pseudobranchia, and spiracle in Ganoids, to those pointed out by Muller (Ganoid, 
p. 135): — 
1. Opercular gill, pseudobranchia, and spiracle : Acipenser. 
2. Opercular gill, pseudobranchia, no spiracle: Lepidosteus. 
3. Opercular gill, no pseudobranchia, no spiracle : Scaphirhjnchus , Lepidosiren , Pro- 
topterus. 
4. No opercular gill, but pseudobranchia and spiracle : Planirostra. 
5. No opercular gill, no pseudobranchia, but spiracle : Polypterus. 
6. No opercular gill, but pseudobranchia, and no spiracle : Ceratodus. 
The Lung (Plate XXXVIII.). 
The pneumatic apparatus of Ceratodus may be described either as a single lung with 
symmetrical arrangement of its interior, or as two lungs confluent into a single sac 
without any trace of a septum. The sac is wide, and extends from one end of the abdo- 
minal cavity to the other ; it occupies the middle of the dorsal region, being firmly 
attached to and along each side of the aorta. Its external surface shows numerous 
small rounded, prominences, corresponding to the minor cells of its cavity, and sur- 
rounded by the network of the pulmonal vein. These prominences are absent in a 
stripe (a) running along the middle of its ventral surface, and bordered on each side by 
the branches of an arterial vessel (/'/'). The minute ramifications of the blood-vessels 
extend only sparingly into this smooth stripe, having probably only a nutritive, and not 
a respiratory function. The attachment between intestine and lung is also most intimate 
along this stripe, which is opposed to the aorta, and indicative of a division of the lung 
into two lateral halves. Such a division is also indicated by a slight prominence in 
front (b), and behind (c). The right half is contracted at its anterior extremity, slightly 
bent towards the right side, and opens, by a very short duct terminating in a glottis ( gl ), 
into the ventral side of the oesophagus, somewhat to the right of the median line. The 
glottis is a slit about one eighth of an inch long, and provided on one side with a dupli- 
cature of the membrane, which acts as a valve. 
The interior of the lung is best seen by cutting it open along the smooth stripe in its 
median line (fig. 2). Both halves are then seen to have an identical and nearly sym- 
metrical structure, being divided into a number of compartments formed by strong trans- 
