50 



;500L()GY 



SECT. 



setting- in at tlie montli, entering tlie pharynx, passing thence by 

 the gill-slits into the atrimii, and out at the atrioporo. The 

 current, as in l^niicata and Balanoglossus, is both a respiratory 



-.-K 



Fn:. 744.— Amphioxus lanceolatus. Diagrammatic transverse section of the pharyn- 

 geal regiuij, passing nii the right thrnugh a primary, on the left through a secondary branchial 

 lamella, ao. dorsal aorta ; <■, derm; '■<■', cndnstjiar portion of cielomi^ ; /: fascia or iuvesUng 

 layer of myomere ; /7i, compartment containing fin-ray ; (/. gonad ; ,'//. glomernliis (modified 

 part of Ijranchial artury in relation tn nL-phridimn) ; i', branchial artery; kd, ]iharynx; W, 

 combined atrial and coalotnic wall (liganientiun denticulaturn) ; )n. myomere ; ml, transverse 

 musv;le ; n. nephridium ; of, metaplcural lymph-spaee ; /?, atrium ; i><-, coelome ; si, ventral 

 aorta; -s/c, sheath of notochord and neuron ; %kj\ spaces in ventral wall. (From Korschelt and 

 Ileidcr, after IJoveri and Hatschek.) 



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 j)haryngcal region, by paired cavities (Fig. 743, ccd., Fig. 742, 



