568 



CHORDATA. 



bulbus ( (?) is a muscular swelling in front of the conus, in the 

 arterial trunk. 



The connexion of ventral and dorsal aortas is effected in young 

 fishes (fig. 597) by the gill arteries directly; later by means of the 

 complicated loops of the gill circulation. When these are de- 



FIG. 596, Forms of hearts of fishes in schematic long section. (After Boas.) A, 



chian and most ganoids; B, Amia; C, Teleost. a, auricle; 6, bulbus arteriosus; c, conus 

 arteriosus; fc, valves; s, sinus venosus; t, truncus aortse; v, ventricle. 



FIG. 597. Head of embryo teleost. (Diagram from Gegenbaur.) a, auricle ; abr, ventral 

 aorta with arterial arches; ad, dorsal aorta; c, carotid ; dc, Cuvierian duct, formed by 

 union of jugular and posterior cardinal veins ; n, nostril ; *, gill clefts ; sv, sinus veno- 

 sus; v, ventricle. 



veloped, afferent branchial arteries, gill capillaries, and efferent 

 arteries can be recognized, the latter uniting to form the dorsal 

 aorta and also giving off the arteries (carotids), which go to the 

 head. 



The nephridia are a pair of large reddish-brown organs lying 

 outside the body cavity to the right and left of the vertebral 

 column, usually extending from heart to anus. Their ducts empty 

 behind the anus or in the dorsal wall of the intestine and are often 

 provided with enlargements called, from their functions, urinary 

 bladders, although totally different morphologically from the 

 urinary bladder of the higher vertebrates. The gonads, suspended 



