MARINE MISCELLANEA. 227 



sponges, hydroid zoophytes and other organisms. As shown in the photograph, the 

 weight of the clustered polyps on their nodulated axes is such as, in most instances, 

 to bend the organisms prostrate when uncovered by the tide, though as soon as the 

 water rises again they assume the vertical position indicated by one of the colony- 

 stocks to the extreme right. 



By carefully detaching some of the polyparies from this rock and examining them 

 on the spot, the mystery of the hitherto seemingly abnormal constitution of their axial 

 cores was revealed by the discovery, within the central hollow of several of them, of an 

 elongate centipede-like worm. This was in some instances as much as a foot in length. 

 The worm belonged to the family of the Nereidse, and in that group to the genus Nereis, 

 of which there are many representatives in British seas. It is a common property of 

 these worms to exude from their body surface a mucilaginous secretion, which hardens 

 in the water to a silk-like consistence. Frequently, layer upon layer is added until the 

 tube assumes a felted texture, or it may have incorporated within its substance particles 

 of sand, shell, or any other contiguous foreign substances. The hollow, zigzag, felted tube- 

 core of Acrozoanthus was the direct product of the enclosed worm, but it owed its 

 erect form and anomalous zigzag shape exclusively to the directing influences of the 

 commensal zoophyte. Lengths of this felted worm tube, but without any attendant 

 polyps, were found adherent to the rock amongst the tangle of seaweeds and other 

 growths that covered it. In this phase they resembled the simple prostrate, cylindrical 

 tubes of the ordinary Nereids. 



As soon, however, as the polyp attaches itself to the growing end of the 

 tube, it appears to impart to the worm a tendency to construct its domicile at a 

 tangent from the basal structure, and thenceforward a sort of zigzag race ensues 

 between the worm and the polyp to get the upper hand. The polype, in fact, by rapid 

 sub-division and spreading of its connecting flesh, or "csenosarc," soon threatens 

 to, and presently does, overgrow the terminal aperture from which the Nereis is wont 

 to thrust its head and tentacular cirrhi, and to fish in the surrounding water. Finding 

 itself baulked in that direction, the worm makes a new start in the same plane, and 

 at a divergent angle of about 60 degrees. Before, however, it has added another inch 

 to its dwelling tube, the polyp has once more overtaken it, and converted its front 

 entrance into a cul-de-sac. This process is repeated again and again with almost 

 mathematical uniformity, and so at length, by the accumulation of a score or so of 

 obliquely ascending gradations, the organism in its complete form, as here photographed, 

 is finally produced. Arriving at this stage, the worm apparently grows tired of being 



