30C) TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



iii fig. 1, from the anterior (a, fig. 1) to the posterior end 

 (p, fig. 1). It is open at both extremities, and usually of 

 a pale yellow or brownish colour, prettily ornamented, 

 more especially towards the two ends, by Y-shaped, or 

 zigzag markings of distinctive tint. These markings are 

 indicative of a very interesting internal structure at either 

 end of the tube, namely, the valves, or diaphragms, which 

 have been noticed, as existing only in Hyctlincecia, by 

 Ehlers and Mcintosh, though their function has not, I 

 believe, been hitherto explained. 



These valves take the form of membranous pockets 

 inside the tube attached to opposite walls, the opening of 

 the pockets directed outwards. Their function is 

 doubtless protective. E ! ach end of the tube is usually 

 guarded by two or more pairs of valves. At the wider- 

 end of the tube the valves (r, fig. 1) are attached at the 

 same level, and closure is effected by their meeting in the 

 middle, but at the narrow end they (V, fig. 1) are not 

 attached at the same level; they consequently become 

 alternate, and, closing more or less nearly on the opposite 

 wall of the tube, give rise to the zigzag marking. 



The worm, travelling along* the sea-bottom in a tube 

 open at both ends, would (except for this provision) be 

 always exposed in the rear to the attack of enemies. 



These valves which, like the valves in a vein, close 

 automatically by the inrush of water, on the retreat of the 

 worm (assisted, probably, by the elasticity of the valves 

 themselves), act as an effectual barrier against foes. 



I have on many occasions been fortunate enough to see 

 this automatic closing of the valves; in fact, it was the 

 perfect resistance which they offered to an attempt to 

 expel the worm that first attracted my attention. 



On the occasion referred to, the attempt was being made 

 with a small syringe applied to one end of the tube: but 



