336 



MANUAL OF ELEMENT Alt Y ZOOLOGY 



animal be fed with carmine the 

 through the nephridia. A pair 



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colouring matter is excreted 

 of funnel-shaped structures, 

 known as brown tubes, 

 which lie in the hinder 

 part of the dorsal ccelom 

 and open into the atrium 

 at their wide ends, have 

 also been regarded as 

 nephridia. 



The blood is colourless 

 / and contains 



System" white cor P us - 



cles. The vas- 

 cular system is closed. 

 There is no heart, but 

 the larger vessels are con- 

 tractile and set up a cir- 

 culation. A ventral or 

 branchial aorta lies in the 

 subendostylar ccelom and 

 gives off to each primary 

 gill bar a vessel which 

 divides to take part in 

 the formation of a rather 

 complicated branchial sys- 

 tem in the primary and 

 secondary bars and synap- 

 ticute. On each side the 

 branches of this system 

 are gathered up into a 

 series of vessels, which 

 open into a longitudinal 

 supr abranchial artery be- 

 side the epibranchial 

 groove, some of the blood 

 passing through nephridial 

 plexuses on the way. Be- 

 hind the pharynx the supra- 

 branchial arteries unite to 

 form a dorsal aorta, which 

 runs back under the noto- 



