BALANOGLOSSUS. 435 



Dolichoglossus, Ptychodera, Schizocardium, and Glandiceps. 

 They are very widely, though locally, distributed, and most 

 occur in the littoral area. 



DESCRIPTION OF BALANOGLOSSUS 



Form and habitat. The species which form this genus 

 are worm-like marine animals, burrowing in sand and mud 

 in almost all seas. They vary in length from about i in. to 

 over 6 in., and are brightly coloured and have a peculiar 

 odour, like that of iodoform. The sexes are distinct, and 

 are marked externally 

 by slight differences in 

 colour. The body con- 

 sists of a prominent 

 turgid and muscular 

 " proboscis," a firm 

 " collar," a region with 

 gill-slits, and, finally, a 

 long, soft, slightly coiled 

 portion. 



Skin and muscles. 

 The epidermis is ciliated, 

 and exudes abundant 

 mucus from unicellular FIG. 234. Male of Balanoglossus (Do- 

 glands. With the addi- lichoglossus] kowalcvskii. After Bate- 

 tion of grains of sand, son - 



fV rY-mr>nc orvm^f irvxao Note anterior proboscis. Mo. t Mouth"; <?/., 



the mucus sometimes slight opercul m behind the <; ollar . then ^ 



forms a tube round the region with gill-slits ; ts., testes ; ., anus. 



body. Some species are 



phosphorescent. The muscular system is best developed 

 about the proboscis and collar, which are used in leisurely 

 locomotion through the soft sand. There are external 

 circular and internal radial and longitudinal muscles. The 

 fibres are unstriped. There is great regenerative capacity. 



Nervous system. The dorsal nerve- cord is most de- 

 veloped in the collar, but is continued along the whole 

 length. It arises as a longitudinal groove of ectoderm and 

 often remains tubular, like a typical spinal cord. The 

 dorsal nerve-cord is connected by a band round the collar 

 with a ventral nerve. There is also a nervous plexus 



