Characteristics of the Vertehrata. Ixi 



developments of the anterior wall of the cloaca, whilst those of the 

 latter consist of two protrusible hollow conical bodies, which opeu 

 into that cavity from behind. In the C/ielonia, two peritoneal 

 canals are j^rolong-ed into the penis, in the distal extremity of which 

 they terminate blindly ; two canals, probably homologous with 

 them, and also with the similarly situated pores of the Selachian 

 and Ganoid Fishes, exist in the GrocodiUna, but open at the base 

 of the intromittent org-an. The testes and ovaries are bilaterally 

 symmetrical, except in the Opliidia, where the right gland is placed 

 anteriorly to the left, and in the females is the larger of the two. 

 The ova often undergo development whilst in the oviducal canals, 

 but the young are not set free from the foetal envelopes before 

 extrusion from the maternal organism. For liberating themselves 

 from these envelopes, the young of the really ovo-viviparous Viper, 

 as also of many other Reptiles, are provided with a temporary 

 premaxillary tooth. All Loricata are oviparous in the strict sense; 

 and amongst the Squamata, nearly allied forms may vary as to 

 being ovo-viviparous or ovii:)arous. 



Some lowly organized Lizards, such as Hatteria, possess the 

 power of reproducing lost portions of the tail. 



The sub-division Loricata, under which are comprised the two 

 orders of CrocodiUna and Chelonia, differs from the sub-division 

 Sqiiamata, comprehending the two orders Sauria and Ojjhidia, in 

 the following particulars besides those already enumerated. Their 

 anal cleft is longitudinal, there is usually some calcareous deposit in 

 the shells of their eggs, their ribs are double-headed in the anterior 

 regions of the body. Setting aside a few points which may be 

 correlated with their aquatic and less active habits, the Loricata 

 may be considered as more highly specialized, and possessed of 

 nearer affinities to the higher Vertebrata than the other sub- 

 division of this class. 



Class, Amphibia. 



Cold-blooded Vertebrata, which for longer or shorter periods, or 

 throughout the whole of their lives, are provided with gills for 

 aquatic, in addition to lungs for aerial respiration, and which even 

 when the gills are permanently I'ctained go through some stages of 

 metamorphosis after being set free from the e^^. Amongst these 



