DII-NOL 401 



cavity, which opens internally into the. pharynx by a number of 

 slits, and communicates externally with the outer world by 

 means of a single vertical gill-slit. 



On the other hand, the Lepidosiren approximates to the 

 Amphibians in the following important points : — ^The heart 

 consists of three cavities, two auricles and a single ventricle. 

 True lungs are present, with a trachea and glottis, returning 

 their blcod to the heart by a distinct pulmonary vein, and in 

 every respect discharging the functions of the lungs of the 

 higher Vertebrates. It is true that the lungs of the Lepidosiren 

 aK merely a modification of the swim-bladder of the other 

 fishes, but the significance of the change of function is not 

 affected by this. Lastly, sometimes, at any rate, there are 

 rudimentary external branchiae placed on the side of the neck. 

 This feature, as will be seen shortly, is characteristic of all the 

 Amphibians, either permanently or in their immature state. 



Upon the whole, then, whilst for the purposes of systematic 

 classification the Lepidosiren must be placed amongst the Fishes, 

 it is not to be forgotten that many of its characters are those 

 of a higher class, and that it may justly be looked upon as a 

 connecting link, or transitional form, between the two great 

 divisions of the Fishes and the Amphibians. 



As regards their distribution and mode of life, two species 

 at least of Lepidosiren are known — the L. paradoxa from the 

 Amazon, and the L. annectens from the Gambia. They both 

 inhabit the waters of marshy tracts, and appear to be able in 

 the dry season to bury themselves in the mud, forming a kind 

 of chamber, in which they remain dormant till the return of the 

 rains. Recently there has been discovered in the rivers of 

 Queensland (AustraUa) a fish which has been described under 

 the name of Ceratodus (?) Fosteri, and which would appear to 

 be very closely related to the Lepidosiren. This singular fish is 

 from three to six feet long, and has the body covered with 

 large cycloid scales. The skeleton is notochordal, all the bones 

 remaining permanently cartilaginous. There is a well-developed 

 operculum, but — as in Lepidosiren — no branchiostegal rays. 

 The tail is homocercal, and the pectoral and ventral fins are 

 supported by a median, many- jointed, cartilaginous rod, with 

 numerous lateral branches on each side. The heart consists of 

 a single auricle and ventricle, with a "Ganoid" bulbus arteri- 

 osus. There are five branchial arches, of the Teleostean type, 

 but cartilaginous. The swim-bladder is single, composed of 

 two symmetrical halves, cellular in structure, with a pneumatic 

 duct and glottis, as in Lepidosiren. The intestine has a spiral 

 valve, arid there are no pyloric caeca. 



