346 REPTILIA. 



Of the Yolk. — In the yolk of the alligator, while in the state of 

 incubation, there is a quantity of oil collected in different parts of its 

 substance; whether this oil is in the yolk before incubation, or is 

 formed from the yolk in the time of incubation, is not in my power at 

 present to determine : this oil can be squeezed into the gut through 

 the duct 1 . 



[Order Chelonia.] 



This may be called one order, of which I shall at present reckon two 

 genera, and of which there are many species. The two genera are, the 

 turtle and the tortoise. "Which should be reckoned first and which 

 second, I cannot at present determine. From the tortoise 2 probably 

 being wholly a land-animal, and the turtle being an animal of the water 

 as well as, if not more so than of the land, it might be thought that 

 the tortoise was nearer to the orders or tribes above them ; but from 

 some circumstances it is rather less so, the turtle having lungs more 

 like those of the bird than the tortoise has. 



Of the first [aquatic Chelonia] there is also a great variety. One 

 tribe, which is probably the largest in number and also in size, includes 

 those which inhabit the sea 3 ; and the other [those which frequent] 

 fresh water 4 , probably rivers, and often ponds. A species of this kind 



rnunication may, however, take place. Injected mercury by the left aorta, hoping 

 the valves might be not so complete, but that the metal would pass into the right 

 ventricle : however, it did not, but it passed freely from the left into the right aorta 

 aud its branches. Then injected mercury into the right auricle and ventricle, but 

 none got into the left ventricle. 



"In the heart of the Crocodilus acutus, injected mercury by the left auricle 

 into the left ventricle, and kneaded the cavity in order to press it through any of the 

 sinuses which might establish a communication between the two ventricles ; then 

 opened the right ventricle, and found some mercury in it ; but on pressing the left 

 ventricle, found that the mercury passed into the right ventricle from the orifice of 

 the visceral aorta, which had received it by the aperture of intercommunication with 

 the aorta from the left ventricle. Upon repeating the pressure on the left ventricle, 

 filled with mercury, none passed into the right ; and on tracing the different sinuses 

 leading from the right ventricle, they all terminated in the parietes of the heart, 

 without communicating with the left ventricle. 



"The orifice of intercommunication between the two aortas is larger in the alligator 

 than the crocodile. But this is the sole medium of the intercommunication between 

 the venous and arterial bloods, which exists in the central organ of circulation. See 

 Preparation No. 921 A, Crocodilus acutus. To convert a crocodile's heart into that 

 of a bird's, stop up the orifice leading from the right ventricle into the visceral aorta, 

 and obliterate that vessel."] 



1 [Hunt. Preps. Phys. Series, Nos. 3364—3374.] 



- [Genus Tesfudo, Cuv.] 3 [Genus Chelonc, Cuv. ] 



* [Genus Emys, Cuv.] 



