546 



PISCES FISHES. 



a jugular vein ; (b) from the liver by a hepatic sinus, which runs from 

 one precaval sinus to the other like the string of the bow ; (c] from a 

 large posterior cardinal sinus (between the reproductive organs) by 

 a cardinal vein on each side ; (d) from the hind-fin by an epigastric, 

 with which brachials from the fore-limb unite anteriorly. The great 

 cardinal sinus receives blood from the hind-limbs, the kidneys, and 

 other posterior parts. 



Blood passes into the liver (a) from the cceliac artery, and (b} by 

 portal veins from the intestine (the hepatic portal system) ; blood leaves 



the liver by hepatic veins which enter 

 the hepatic sinus. 



Blood passes into the kidneys (a) 

 from the renal arteries, and (b) by 

 renal portal veins from the caudal, 

 pelvic, and lumbar regions (the renal 

 portal system) ; blood leaves the . 

 kidneys by posterior cardinal veins, 

 which enter the cardinal sinus. 



Into the precaval sinus there also 

 opens the lymphatic trunk. 



The heart lies in a pericardial 

 cavity, which is connected with the 

 abdominal cavity by two fine canals, 

 and is an anterior part of the coelom. 

 The blood contains, as usual, red 

 blood corpuscles 'and leucocytes. 



The dark red spleen lies in the 

 curve of the stomach. The red 

 thyroid gland lies just in front of 

 the anterior end of the ventral aorta. 

 The thymus is represented by a 

 whitish body dorsal to each of the 

 first four gill-clefts. Each begins as 

 a patch of endoderm, and this is 

 invaded by migratory mesenchyme 

 288. Urogenital organs cells which multiply as lymphocytes. 



g.s. 



-Cl. 



FIG. 



of male skate. 



v.d., 



7 1 ., Testis ; Ep.> epididymis ; 

 vas deferens ; K., kidney ; 

 seminal vesicle ; s.s. t sperm sac ; 

 u.g.s., urogenital sinus; C/., cloaca. 



Excretory and reproductive 



systems. The dark red kid- 

 neys lie far back on each 

 side of the vertebral column. 

 They are developed from the hind part of the mesonephros. 

 Several tubes from each kidney combine to form a ureter. 

 The two ureters of the male open into the urogenital 

 sinus, whence the waste products pass out by the cloaca 

 in the female they open into little bladders, the dilated 

 ends of the Wolffian ducts, and thence by a common 

 aperture into the cloaca. 



