Ixiv Introduction. 



and to the posterior parts of the body respectively and to the kings, 

 it provides for the more or less perfect separation of the streams of 

 arterial and venous blood received from the two auricles. All Am- 

 phibia possess a renal-portal system, the factors of which anastomose 

 freely with those of the true portal system. This latter system 

 always receives, by the intermediation of the epigastric veins, an 

 important factor from the allantoid bladder ; by which connection 

 the connection of the umbilical and placental veins, as seen in 

 Mammals, is very obviously foreshadowed. The transpirable and 

 glandular character of the skin would appear to confer an aerating 

 function upon the vascular ramifications which it contains in great 

 abundance. The lymphatic vessels are greatly developed in the 

 subcutaneous spaces ; and lymphatic hearts are present in the 

 Amira, both upon the anterior and upon the posterior junctions of 

 this system to the blood-vascular. In the Urodela, as in Reptiles, 

 the posterior hearts only exist. In the higher Amphibia, two sets 

 of gills are developed. One of these is the external set which 

 corresponds to the permanent gills of the Perennibranchiate Am- 

 phibia, and to the deciduous external gill filaments of the Plagio- 

 stomous Fishes, which latter it resembles in being shed early. 

 The other is the internal set which are developed subsequently to, 

 and retained in the Urodela and Anura longer than the ciliated 

 external set. In certain Amphibia [Menopo7na, Amphmma, Crypto- 

 hranchus, thence called Derotremata), a fissure remains in the pha- 

 ryngeal walls after the shedding of the branchiae. This event does 

 not always take place at the same date in the life of the larva. 



Cartilages representing a larynx are developed round the inlet 

 from the pharynx into the air passages. There is a trachea of con- 

 siderable length in Menopoma, Amphmma, and the Caec'diae ; and 

 there are bronchi of considerable length in Pipa and Bactyletlcra ; 

 but ordinarily, these tubes are only rudimentarily represented in 

 Amphibia. 



The Amphibia appear to have no secondary kidney developed; 

 and the products of the urinary and sexual glands are always dis- 

 charged into a cloaca by a single orifice, that of the duct of the 

 Wolffian body, on either side. In Troteus, the transversely running 

 ducts of the primary kidney remain distinct from each other, up to 

 their junctions with the antero-posteriorly running duct of the 

 primary kidney, the so-called ' Miiller's duct.' In other Amphibia, 



