PLATE XXIV. 



CIRCULATION IN THE TADPOLE (after Whitney). 



Fig. 1. Anterior portion of young: Tadpole, showing the external gills, with the incipient tufts of 

 the internal gills, and the pair of minute tubes between the heart and the spirally-coiled intestine, 

 which are the rudiments of the future lungs. 



2. More advanced Tadpole, in which the external gills have almost disappeared : a. remnant of 

 external gills on the left side; 6, operculum; c, remnant of external gill on the right side, turned in. 



o. Advanced Tadpole, showing the course of the genera] Circulation: a, heart; 6, branchial 

 arteries; c, pericardium; d, internal gill: e, first or cephalic trunk; /. branch to lip; g, branches to 

 head; h, second or branchial trunk ; i, third trunk, uniting with its fellow to form the abdominal 

 aorta, which is continued as the caudal artery fc, to the extremity of the tail ; I, caudal vein ; in, 

 kidney ; n, vena cava ; o, liver ; p, vena portae ; q, sinus venosus, receiving the jugular vein, r, 

 and the abdominal veins, t , u, as also the branchial vein, v. 



4. The branchial Circulation on a larger scale: A, u. c, three primary branches of the branchial 

 artery; a. cartilaginous arches; 6, additional frame wo/k; c, e, twigs of branchial artery; d, f, root- 



5. Origin of the vessels of the internal gills, g, from the roots of those of the external. 



6. The heart, systemic arteries, pulmonary arteries and veins, and lungs, in the adult Frog; the 

 heart being turned up in the right-hand figure, to show the junction of the Pulmonarv veins and 

 their entrance into the left auricle 



