158 ZOOLOGY. 
which is digestive, and leads directly to the intestine behind. | 
This pharyngeal respiratory portion of the digestive canal has 
on each side, in each segment, a dorsal sac, the two commu- 
nicating along the median line of the body. The dorsal re- 
spiratory sacs bear in their walls a delicate chitinous gill- 
support or arch. Between the gill-arches, forming numerous 
lamelle, are a series of slits, leading on each side to open- 
ings (spiracula) situated dorsally. The water passes through 
the mouth into each gill-sac, and out by the spiracles. The 
nervous system lies above a notocord. There is a dorsal 
vessel, which sends branches to the respiratory sacs, and a 
Fie. 108. 
Fig. 108.—Balanoglossus, not fully mature; magnified. 
Fig. 199.—Larva (7ornaria) of Balanoglossus. a,anus; 6, branch of water-vascu- 
lar system leading to the dorsal pore /d); ¢, eye-speck ; g, gills ; , heart ; 4, in- 
testine; m, mouth; m’, muscular band from the eye to the water-vascular tube ; 0, 
cesophagus ; s, stomach or alimentary canal ; u, lappet of stomach ; w’, anal band of 
cilia ; w, water-system.—After A. Agassiz. 
ventral vessel. The worm lives in sand at low-water mark 
from ‘Cape Ann to Charleston, 8. C. 
The life-history of this worm is most interesting. The 
young, originally described under the name of Tornaria, 
was supposed to be an Echinoderm larva, though it closely 
resembles the larval Gephyrea and Annelides. It is a trans- 
parent, minute, ciliated, slender, somewhat bell-shaped form 
(Fig. 109), with black eye-specks. When transforming to 
the worm condition, a pair of gills arise on sac-like out- 
growths of the esophagus, and afterwards three additional 
