442 



THE DOGFISH 



With regard to the general morphology of the blood-system, the 

 dorsal aorta with the caudal artery may be considered as a dorsal vessel 

 (C07iipare Earthworm, p. 329, Crayfish, p. 365, and Amphioxus, Fig. 

 loi) ; 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. 



The blood, like that of the frog (pp. 104 — 106), con.si.sts 

 of a colourless plasma containing red corpuscles — the colour 



'k^. 114. — Diagram illustrating the course of the circulation in the dogfish. Ves^elb 

 containing oxygenated blood red ; non-o,\>'genated blood blue. 

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

 the kidneys ; I., of the liver ; T. of the tail. a. br. ti. afferent branchial arteries ; 

 ail. auricle ; l". a. conns arteriosus ; d. ao. dorsal aorta ; c. br. a. afferent branchial 

 arteries ; /;. /. v. hepatic portal vein ; It. v. hepatic vein ; h. lacteals ; ly. lymph- 

 atics ; p7'. cv. V. precaval vein ; r. p. v. renal portal veins ; j. 7'. sinus venosus ; 

 V. ventricle ; li. ao. ventral aorta. The arrows show the direction of the current. 

 (From Parker and HaswcU's Zoology.') 



of which is due to hsemoglobin — and leucocytes. It must be 

 remembered that the ventral aorta and the afferent branchial 

 arteries (Fig. 114), like the pulmonary artery of the frog 

 (p. 144), contain venous blood. As in the frog, there are 

 in addition to the blood-vessels, a set of lymphatic vessels. 



Nervous System. — The nervous system is constructed on 

 a similar plan to that of the frog (compare Part I, Chapter X) 



