378 Dr. A. Giinther's Description 0/ Ceratodus. [Mar. 16, 



ways, for instance by Mr. Parker as the " large first pharyngo-branchial." 

 Arrangement and detachment of dermoneurals as in Lepidosiren. 



The scapular arch and pelvis are more developed than, but typically 

 entirely identical with, those of Lepidosiren. 



The paddles are supported by a cartilaginous axial skeleton, that is, by 

 a longitudinal series of joints, with lateral divergent articulated branches, 

 each joint having two of these branches. The relations of this singular 

 structure to the corresponding parts in Lepidosiren and Selachians are 

 explained ; and there is no doubt that the Ganoids of the Devonian epoch, 

 with acutely lobate fins, had their paddles supported by a similar internal 

 skeleton. 



Eye without falciform process or choroid gland. 



Heart. — The arrangements of the interior of the ventricle and single 

 atrium, and the external appearance of the bulbus arteriosus, are very 

 similar to the same parts in Lepidosiren ; but the valvular arrangement of 

 the bulbus is more " Ganoid," though considerably modified. We find at 

 a short distance from the origin of the bulbus, first, a single, cartilaginous, 

 papillary valve worked by a special muscle, then a transverse series of four 

 small short valves (sometimes reduced to papillae), then a transverse 

 series of four oblong raised strips (rudimentary valves), finally a transverse 

 series of four well-developed " Ganoid " valves. Four arcus aortce enter 

 the four gills, without sending off branches, and four vence branchiales 

 are collected into the aorta descendens. 



A description of the principal portions of the circulatory system follows. 



The gills are completely developed, four in number, lamellated. The 

 pseudobranchia does not receive its blood from the heart ; thus an " oper- 

 cular gill " is absent as well as spiracles. 



The lung is single, but its cavity divided into two symmetrical halves, 

 each with about thirty cellular compartments ; pneumatic duct and glottis 

 as in Lepidosiren ; its dorsal artery is a branch of the A. cceliaca ; and its 

 vein enters the atrium separately from the sinus venosus. 



The most important points of the structure of the remaining soft organs 

 are the following : — the intestinal tract is perfectly straight and very 

 wide, with a complete spiral valve, along the axis of which large glands 

 are imbedded ; the stomach is indicated only by a shallow double pyloric 

 fold ; there are no pyloric appendages, but a glandular mass appears to 

 represent the spleen. Not only the liver, but also the paired, lobed 

 kidneys are provided with a portal system. The two ureters enter by a 

 single opening a small urinal cloaca situated at, and partly confluent with, 

 the back of the rectum. Testicles without developed vas deferens, which 

 appears to be represented by a blind duct, traversing the interior of the 

 testicle, and receiving the semen from the canaliculi seminiferi. Ovaries 

 transversely laminate, the laminae being the bearers of the stroma in which 

 very small ova are developed ; the ova fall into the abdominal cavity, and 

 are expelled by a pair of wide peritoneal slits behind the vent. But there 



