50 



/< )( )LOGY 



SECT. 



setting in at the mouth, entering the pharynx, passing thence by 

 the gill-slits into the atrium, and out at the atriopore. The 

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



1 



FIG. 744.VAmphioxus lanceolatus. Diagrammatic transverse section of the pharyn- 

 geal Region, passing on the right through a primary, on the left through a secondary branchial 

 lamella, ao. dorsal aorta ; c, derm; ec, enrlost3 r lar portion of coelome; /'. fascia or investing 

 layer of myomere ; //&, compartment containing fin-raj 7 ; ;/. gonad ; <jl. glomeruhib (modified 

 part of branchial artory in relation to nephridiinn) ; k, branchial artery ; kd, pharynx ; Id, 

 combined atrial and ctelomic wall (ligamentum denticulatum) ; m. myomere ; int. transverse 

 muscle ; n. nephridium ; of, metapleural lymph-space ; p, atrium ; sc, ciL-lome ; gi, ventral 

 aorta ; sh, sheath of notoehord and neuron ; uf, spaces in ventral wall. (Prom Korschelt and 

 Heider, after Boveri and Hatschek.) 



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

 organisms in the surrounding water. 



Ccelome. Owing to the immense size of the atrium the body- 

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

 in the pharyngeal region, by paired cavities (Fig. 743, ccel., Fig. 742, 



