50 



ZOOLOGY 



SECT. 



settiiie^ in at the month, entering the phaiynx, passing- thence by 

 the gill-slits into the ati'inni, and out at the atriopore. The 

 current, as in Tunicata and Balanoglossus, is both a respiratory 



aa 



'.-^/f 



Fici. 714. — iVmphioxus lanceolatus. Diagi-aminatic transverse section of tlie pharyn- 

 geal region, passing on therigiit through a primary, on the left thiough a secondary branchial 

 lamella, ao. dorsal aorta ; f, derm ; ec, eudostylar portion of ctelome ; ;; fascia or iii vesting 

 layer of myomere ; /A, compartment containing fin-ray ; </. gonad ; <\l. glo)nonilus (modified 

 liai-t of hranchial artery in relation to nephridium) ; k, branchial artery; i-<?, pharynx; Id, 

 combined atrial and ccelomic wall (ligamentum denticulatiim) ; m. mj-omere ; mt, transverse 

 musc'le ; /!. nephridium ; of, metaplcinal lymph-space ; /;, atrium ; sc, cfjelome ; si, ventral 

 aorta; ^k, sheath of notochord and neuron ; %'/, spaces in ventral wall. (P'rom Korschelt and 

 Hcider, after Bovcri and HattAck.) 



and a food-current, the animal feeding passively on the minute 

 organisms in the surrounding water. 



Coelome. — Owing to the immense size of the atrium the body- 

 cavity, which is a true coelome, is much reduced. It is represented, 

 in the pharyngeal region.by paired cavities (Fig. 748, ca'/., Fig. 742, 



