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, Ptychodera, 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. 



FIG. 124. Male of Balanoglossus 

 Kowalevskii. (After BATESON.) 



Note anterior proboscis; Mo., mouth; 0/., 

 slight operculum behind the collar; then the 

 region with gill slits ; /s., testes ; a., anus. 



Skin. 



The epidermis is ciliated, and exudes abundant mucus 

 from unicellular glands. In B. robinii the mucus 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 



