392 



HEMICHORDA OR ENTEROPNEUSTA. 



of the adult, and is compared to the anterior unpaired body 

 cavity ^Amphioxus. 



Spengel, in his recent monograph, recognises 19 species 

 and 4 genera — Balanoglossus, Ftychodera, Schizocardium, 

 and Glandiceps. They are very widely, though locally, dis- 

 tributed, except, perhaps, on the Pacific coasts of America. 



Description of Balanoglossus. 



Habit. 

 The species which form this genus are worm-like marine 

 animals, found in sand and mud in the English Channel, 

 the Mediterranean, 

 Chesapeake Bay, &c. 

 They vary in length 

 from about an inch to 

 over six inches, and 

 are brightly coloured 

 and of a peculiar 

 odour. The sexes 

 are distinct, and are 

 marked externally by 

 slight differences in 

 colour. 



Form. 

 The worm-like body 

 consists of a promi- 

 nent pre-oral region 

 or "proboscis," a firm 

 "collar" behind the mouth, behind this a region with gill 

 slits, and finally, a long, soft, slightly coiled portion. 



Skin. 

 The epidermis is ciliated, and exudes abundant mucus 

 from unicellular glands. In B. robinii the muci'c sets 

 firmly, and, with the addition of grains of sand, forms a 

 tube round the body. Some species are phosphorescent. 



Muscular System. 

 The muscular system is best developed about the pro- 

 boscis and collar, which are used in leisurely locomotion 



Fig. 124.- 

 Kowalevskii. 



-Male of Balanoglossus 

 (After Bateson.) 



Note anterior proboscis; Mo., mouth; op., 

 slight operculum behind the collar; then the 

 region with gill slits ; ts., testes ; a., anus. 



