490 HEMICHORDA 



like a lob-worm, no limbs like a sea-mouse. The body con- 

 sists of a " proboscis " in front of the mouth, a firm "collar" 

 region behind the mouth, then a region with gill-slits, and 

 finally, a soft slightly coiled portion. But peculiar as they 

 are in outer form, they are still more peculiar internally. It 

 is enough in this introductory note to say that they have got 

 remarkable gill-slits, a dorsal as well as a ventral nerve, a 

 strange dorsal piece of skeleton in the front of the body. 

 They vary in length from about I in. to over 6 in. ; they are 

 often coloured — red, brown, greenish — and they are occasion- 

 ally phosphorescent ; the skin is ciliated all over and is rich 

 in unicellular glands secreting mucus which, with the ad- 

 dition of grains of sand, sometimes forms a tube around the 

 body ; they have a pungent odour like iodoform (possibly of 

 protective value) ; underneath the skin there is a muscular 

 body-wall, but the fibres are of the unstriped variety, which 

 means that they are slowly contracting ; thus the locomotion, 

 which is helped by the external cilia, by the proboscis, and by 

 the engulfing of sand by the ever open mouth, is leisurely ; the 

 food consists of the organic particles and small organisms in the 

 sand. 



A vivid picture of the occasional activity of Enteropneusts 

 is given by Iwaji Ikeda in a paper entitled " On the Swimming 

 Habit of a Japanese Enteropneust, Glandiceps hacksii Marion " 

 {Annotationes zoologicce Japonenses, vi.. 1908, pp. 255-257). 

 " Very early in the morning of 3rd September, 1907, when I 

 was out skimming with some of my students a short distant off 

 Sesuijima (near Tomo, about 50 miles E. of Hiroshima) in the 

 Inland Sea, a curious sort of plankton covering a considerable 

 area attracted our notice. On examining the contents of our 

 net, it turned out to be swarming Balanoglossus. A little later, 

 when the sun was about to rise, we could perceive myriads of 

 lively swimming specimens about our boat. We now came to 

 realise that we had been rowing about in a big sheet of swarm- 

 ing Enteropneusts. More than delighted with this sight, we 

 collected a bucketful of specimens — a task accomplished in but 

 a minute. They measured from 3 to 15 centimetres in length 

 (8 centimetres on an average). The belt-like zones of this 

 plankton varied from 1 to 5 metres in width and were in some 

 cases 2 metres in thickness. The animals were crowded in 



