40 WONDERS OF ORGANIC LIFE. 



generators of caloric. In cold-blooded reptiles 

 and fishes, the structure of the heart, and the 

 condition of the arterial blood, are different 

 from those of quadrupeds and birds. In rep- 

 tiles, the heart consists of but one ventricle and 

 two auricles ; and of the latter, the right auricle 

 receives the vitiated blood returned from the 

 system to the heart, the left auricle the arte- 

 rialized blood from the lungs. Both auricles 

 convey their contents into the cavity of the 

 single ventricle. This ventricle (the interior 

 of which, from the interlacement of muscular 

 fibres, termed fleshy columns, or carnem columnar, 

 assumes an almost spongy appearance) re- 

 ceives, therefore, both vitiated and arterial ized 

 blood, and these become more or less mixed 

 together. Part of this mixed fluid is sent 

 through the aorta to supply the system, and 

 part through the pulmonary arteries to the 

 lungs, to undergo a further degree of oxygena- 

 tion — this ventricle having both the systemic 

 and pulmonic arteries originating from it. 

 Such is the routine of the circulation in the 

 more perfect of the reptile class, -namely, tor- 

 toises, lizards, and snakes. In the amphibia, as 

 frogs, newts, the siren, etc., the circulation is 

 that of a fish during the primary stage of their 

 existence ; and in some, as the siren and pro- 

 teus, continues to be such through life, although 

 lungs are also given, but are in little actual 

 use. In fishes, the ventricle receives the blood 

 from the single auricle, and by its contraction 

 transmits it into an enlarged arterial vessel, 



