10 



MORPHOLOGICAL TYPES 



The gut is suspended by a dorsal mesentery, and its lining is 

 ciliated. It is surrounded by a thin coat of smooth muscle. 



The side walls of the pharynx are perforated by a large 

 number of gill-slits, openings which slant forwards from 

 below up. For this reason several gill-slits will be cut in a 

 single transverse section. 



Ciliary Mode of Feeding. — Along the whole length of the 

 dorsal wall of the pharynx runs a ciliated groove known as the 



b.«gEE 



Fig. 7. — Amphioxus : transverse 

 section through the endostyle 

 showing the cilia, the four 

 tracts of glandular cells (gc), 

 the subendostylar coelom (se), 

 and the ventral aorta (va). 



Fig. 8. — Amphioxus : transverse section 

 through two primary (pg) and one 

 secondary (sg) gill-bars. 



ae, atrial epithelium ; b, blood-vessel ; 

 c, coelomic cavity in the primary gill- 

 bars ; sk, skeletal rods of the gill-bars. 



hyperpharyngeal groove. Anteriorly this groove connects 

 with two tracts of ciliated cells, the peripharyngeal bands 

 which pass round one on each side behind the mouth and 

 down to the floor of the pharynx. There they join the endo- 

 style, which extends all the way back through the pharyngeal 

 region. The endostyle consists of four tracts of glandular 

 cells, separated by tracts of ciliated cells. The glandular cells 

 secrete a sticky mucus which, by the action of the cilia, is 



