•20 ORGANIZATIONOFREPTILES. 



sacs, observed first by Miiller of Bonn and then by Panizza,* for the propulsion of 

 the fluid they convey. 



4. Organs op Circulation. — In the Zoophytes, and lovpest classes of animals, 

 the nutritious parts of the food pass at once from the sac forming their organ of 

 digestion, into the different structures of the body, and become mtegral parts of 

 the animal; but in the higher classes, another change, besides that of digestion 

 must take place in the aliment — a further process of assimilation must be under- 

 gone, before it can nourish the living and organized body. This requires the aid 

 of two different sets of organs, those of circulation and those of respiration; the 

 one set for conveying the blood, the other to complete its assimilation. In Reptiles, 

 the nutritious part of the aliment is taken from the intestinal canal, the great 

 reservoir of food, by the lacteal vessels; it is then introduced through the venous 

 system into the organs of circulation, which vessels are afterwards to carry it to 

 all parts of the body, where it becomes identified with its organs, aiding in their 

 developement, in the restoration of their particles, and affording certain secretions 

 for glands. The organs of circulation in Reptiles vary even more than those of 

 digestion from the type of the Mammalia. In the higher classes of animals we 

 have a double heart; one side for the circulation of venous blood, the other for 

 the circulation of arterial. In the Reptiles we find a simple heart, or the two 

 systems of black and red blood communicating freely with each other. 



The heart is small in proportion to the body, and is always placed near the 

 respiratory organs, they being so constantly and intimately connected with each 

 other, that it may be said, one set of organs modifies the other. Though producing 

 in all nearly the same results on the blood, the structure of the heart varies in the 

 several orders; great differences being observed even in different genera. In the 

 Chelonian Reptiles it is short and thick, having two auricles, the right being the 

 larger; and one ventricle, with thick muscular walls and several cells, all commu- 



* Sopra il Sist. Linf. dei Rettili: Pay. 1833. These cavities will be described in our special 

 anatomy of the genera. 



