200 



ZOOLOG Y. 



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 

 lamellae, 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 



. 138. 



139. 



Fig. 138. Balanoqlos&is:, not fully mature; magnified. 



Fig. 139. Larva t 7'ornariat of Balanoglossw. a. anus ; b, branch of water-vascu- 

 lar systam leading to the dorsal pore (d); e, eye-speck ; ff, gills ; h, heart : i, in- 

 testine: m, mouth; m', muscular hand from the eye to the water-vascular tube ; o, 

 cesophagu* ; x. s'oraach or alimentary canal ; u, lappet of stomach ; u\ 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, S. 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. 139), with black eye-specks. When transforming to 

 the worm condition, a pair of gills arise on sac-like out- 

 growths of the 03sophagus, and afterwards three additional 



