428 NATURAL HISTORY AND ANATOMY OF 



On keeping the Echiurus alive in a vessel of sea-water, it 

 was continually changing its form, swelling itself out in various 

 parts so as to assume very strange and eccentric shapes. If 

 a fresh supply of salt water was poured into the vessel, it 

 would on a sudden become very vivacious, starting up to- 

 wards the surface, and swimming with spiral contortions in 

 the manner of an annelidc. Then it would sink to the bottom 

 of the vessel, and swell itself out with water. 



The Echiurus, like the Thalasscma, was first figured and 

 described by Pallas, who obtained it from the coast of Bel- 

 gium. He gave a most accurate general representation of it, 

 but strangely omitted the true proboscis ; and by all writers 

 since his time the sheath has been described as a proboscis 

 not only in this case, but in the descriptions of most of the 

 other Thcdassemaccce. 



Montagu first perceived the true relation of the Thalas- 

 scma, and remarks in his paper that it should immediately 

 precede Holothuria. This view of its position was also held 

 by Cuvier, and more lately by Brandt. Lamarck, however, 

 placed the Thalasscma and Echiurus in his first division of 

 annelidcs, characterised by having no feet, and including the 

 families Hiruclincs and Echiurccc. In the latter, associated 

 with the earthworm and cirratulus, we find these animals 

 before us. Many zoologists since his time have looked upon 

 them as worms, but the structural details which follow will 

 show that their relation to the annelides is one of analogy 

 and not of affinity, and that their true position is among the 

 Echinodcrmata in the order of Vcrmigrada, or Si^iunculida}* 



Echiurus — Digestive System. 



The digestive tube commences by a mouth of a rounded 

 form, very small in the state of contraction, funnel-shaped 

 when dilated. The oral orifice is continuous with a canal 



* See Forbes's British Echinodcrmata. 



