207 



through the conns." Preceding this Brnner states : "The conus of the 

 Salamandrina shows the same general structure as that we found in the 

 conns of the Salamandra. A spiral valve is distinctly recognizable in the 

 lungless form." (Salamandra has lungs; Salamandrina has none.) 



This point in the comparative anatomy of the amphibian circulation 

 I hold to be an excellent objection to the described course of the blood 

 through the frog heart. 



4. Experimental evidence on the amphibian circulation leaves much 

 still to be done. Mayer found that if the tip of the ventricle was cut off 

 the blood issued in two distinct streams. This, in addition to the colora- 

 tion in the beating frog heart, seems to hold for a segregation of the 

 venous and arterial blood in the spongy ventricle. But Gompertz's experi- 

 ments also seem to indicate that even if this be true a mixing must occur 

 in the vessels. 



The step from the amphibian to the class of Dipnoi is not a very great 

 one, and still we find something which may throw light on the character 

 of blood circulating in the fish. According to Wiedersheim "in Ceratodus 

 the conus arteriosus is provided with eight rows of valves and begins to 

 be divided into two chambers. In Protopterus this division is complete, 

 so that two currents of blood, mainly arterial and mainly venoxcs re- 

 spectively, pass out from the heart side by side. The former comes fnm 

 the pulmonary vein, from which it passes into the left atrium, thence ink- 

 the left portion of the ventricle, and thence to the two anterior branchial 

 arteries. The venous current, on the other hand, passes from the right 

 portion of the ventricle into the third and fourth afferent branchial ar- 

 teries and thence to the corresponding gills, where it becomes purified ; it 

 reaches the aortic roots by means of the efferent branchial arteries. The 

 paired pulmonary artery, like the corresponding vessel in the crossopteryg- 

 ians, arises from the fourth efferent branchial in Ceratodus, and from the 

 aortic root in Protopterus and Lepidosiren." 



There appears to be a physiological flaw in this description unless the 

 fish blood behaves quite differently from that in other animals. Under 

 the assumption that the blood in the fish becomes fully oxygenated in its 

 passage through the gills, the blood carried to the lungs from the efferent 

 branchial artery would already be charged with oxygen, and in this case 

 the lungs would only be functional when the fish is hibernating in the 

 dried mud. Under the assumption that the fish blood is not fully oxj T - 

 genated in its passage through the gills, the lungs would be accessory to 



