546 GENERAL CHARACTERS OF REPTILES. 



with it a true aorta ; of which certain branches, that are sent 

 to the lungs, are developed at the same time, and establish the 

 pulmonary circulation. Finally, the branchial vessels are oblite- 

 rated, and then the circulation becomes almost the same as in 

 other Reptiles (Fig. 324). The venous blood returning from 

 every part of the body, is poured into the ventricle by one of 

 the auricles, and is there mixed with the arterial blood coming 

 from the lungs, and forced into the same ventricle by the 

 other auricle. This mixture then passes into the aorta ; a 

 small part of it being distributed to the lungs, and a larger part 

 to the different organs of the animal. 



483. Certain Batrachians undergo less complete metamor- 

 phoses. Thus Salamanders, like Frogs, acquire members in the 

 progress of time and lose their gills ; but they also preserve 

 their long tail (Fig. 344) : and, as we have already stated, 

 there are also some of these Reptiles which, as regards their 

 mode of respiration, always remain in the tadpole state ; for 

 their gills are preserved during the whole of life, and the deve- 

 lopment of the lungs is stopped at an early stage. It is one of 

 the most curious proofs of the influence of external conditions 

 upon the development of animals, that, by seclusion from light, 

 and by being kept at a low temperature, the common Tadpole 

 may be prevented from changing into a Frog, and may be made 

 to continue to grow as a Tadpole. 



484. In general, Reptiles abandon their eggs as soon as they 

 have laid them ; and they are hatched by the aid of atmospheric 

 warmth only ; but there is in this respect a remarkable excep- 

 tion ; a large Serpent of India, nearly allied to the Boas and 

 Colubers, known by the name of Python, twines itself round its 

 eggs ; and whilst it remains rolled round its offspring, it gives 

 out such a considerable amount of heat, that the temperature of 

 its body is sometimes raised to more than 104 Fahr. Another 

 Reptile, nearly allied to the Toad, the Pipa (Fig. 325), also pre- 

 sents a peculiarity of habit, which deserves to be noticed here. 

 This animal, in its adult state, lives on the earth ; but it is born 

 in the form of a Tadpole, and requires to be then immersed in 

 water. When the eggs are laid, the male places them upon the 



