BALAJSrOGLOSaUS. 199 



lives under stones at or below low-water mark on the coast 

 of New England southwards to South Carolina. 



Order 2. Enopla. — In the members of this group the 

 proboscis is furnished with a style. Eepresentatives of the 

 order are the species of Tetrastemma {T. serpentinum 

 Girard; Fig. 137) and of Nemertes. The former is a little 

 yellowish worm, common under stones on the coast of New 

 England between high and low- water mark ; it has a slightly 

 marked head with four dark eye-specks. 



Class VI.— NEMERTINA. 



Body ribion-Uke or cylindrical, soft, extensible, ciliated externally, with 

 a proboscis in a sheath opening by a pore situated above the mouth. Cir- 

 culatory system approaching that of the Annulata. Sexual organs, duet- 

 less sacs; either with or mth/>ut a metamorphosis. 

 Order i. Anopla. — Proboscis without a style. (Lineus, Mpckelia.) 

 Order 3. Bnopla. — Proboscis witli a style. (Nemertes, Malacobdella.) 



Class VII. — Entekopneusta {Acorn-tongue worms). 



General Characters of the Enteropneusta. — -The re- 

 markable worm, Balanoglossus (Fig. 138), the type of this 

 class, combines characters peculiar to itself, with features 

 reminding us of "the Nemerteans, Annelids, Tunicata, and 

 even the vertebrate AmpMoxus, while its free-swimming 

 larva was originally supposed to be a young Echinoderm. 

 From the fact that the central nervous system lies above a 

 notocord, Bateson places it next to the Vertebrates. 



Balanoglossus aurantiacus (Girard, Fig. 13a) is a long, 

 cylindrical, soft, fleshy worm, footless, without bristles, but 

 with a large, soft, whitish tongue-shaped proboscis in front, 

 arising dorsally within the edge of the collar surrounding 

 the mouth. At the beginning of the digestive canal is a 

 series of sac-like folds, of which the upper or dorsal portion 

 is respiratory, and separated by a constriction from the lower, 



