458 



THE DOGFISH 



CHAP. 



higher order or in the heart. But the hepatic and renal 

 portal veins end in capillaries after the manner of arteries, 

 and the efferent branchial arteries begin in capillaries after 

 the manner of veins. 



With regard to the general morphology of the blood- 

 system, the dorsal aorta with the caudal artery may be 

 considered as a dorsal vessel (compare Earthworm, p. 337, 

 Crayfish, p. 379, and Amphioxus, Fig. no) ; the caudal 

 vein, hepatic portal vein, and ventral aorta as together 

 representing a ventral vessel ; the afferent and efferent 

 branchial arteries as commissural vessels ; and the lateral 

 veins as lateral vessels. It will be seen that the heart of 

 Vertebrates is a muscular dilatation of the ventral vessel, 

 as is also shown by a study of its development (p. 597). 



The blood, like that of the frog (pp. 104-106), con- 

 sists of a colourless plasma containing red corpuscles (the 



FIG. 123. Diagram illustrating the course of the circulation in the Dogfish. Vessels 



containing oxygenated blood red, non oxygenated blood blue. 

 B. capillaries of the body generally ; E. of the enteric canal ; G. of the gills ; K. 

 of the kidneys ; L. of the liver ; T. of the tafl. a. br. a. afferent branchial 

 arteries ; au. auricle ; c. a. conus arteriosus ; d. ao. dorsal aorta ; e. br. a. 

 efferent branchial arteries ; h. p. v. hepatic portal vein ; //. t;. hepatic vein ; Ic. 

 lacteals (p. 98) ; ly. other lymphatics ; pr. cv. v. precaval vein ; r. p. v. renal 

 portal veins ; s. v. sinus venosus ; v. ventricle ; v. ao. ventral aorta. The arrows 

 show the direction of the current. (From Parker and Haswell's Zoology.) 



colour of which is due to haemoglobin) and leucocytes. 

 It must be remembered that the ventral aorta and 

 the afferent branchial arteries (Fig. 123), like the 

 pulmonary artery of the frog (p. 144), contain venous 

 blood. As in the frog, there is, in addition to the blood- 

 vessels, a system of lymphatic vessels 



