PENNA TULID^. 243 



gonia, throws some curious light on the habits of these creatures. 

 "This zoophyte consists of a thin, straight, fleshy stem, with alternate 

 rows of polypi on each side, and surrounding an elastic stony axis, 

 varying in length from eight inches to two feet. The stem at one 

 extremity is truncate, but at the other is terminated by a vermiform 

 fleshy appendage. The stony axis, which gives strength to the stem, 

 may be traced at the extremity into a mere vessel filled with granular 

 matter. At low water, hundreds of these zoophytes might be seen 

 projecting like stubble, with the truncate end upwards, a few inches 

 above the surface of the muddy sand. When touched or pulled, 

 they suddenly drew themseves in with force, so as nearly, or quite, to 

 disappear. By this action, the highly elastic axis must be bent at the 

 lower extremity, where it is naturally slightly curved ; and I imagine 

 it is by this elasticity alone that the zoophyte is enabled to rise again 

 through the mud. Each polyp, though closely united to its brethren, 

 has a distinct mouth, body, and tentacula. Of these polyps, in a 

 large specimen there must be many thousands, yet we see that they 

 act by one movement. They have also one central axis connected 

 with a system of obscure circulation, and the ova are produced in an 

 organ distinct from the separate individuals. For," adds Mr. Darwin, 

 in a note, " the cavities leading from the fleshy compartments of the 

 extremity were filled with a yellow pulpy matter which, under a 

 microscope, consisted of rounded semi-transparent grains aggregated 

 together into particles of various sizes. All such particles, as well as 

 separate grains, possessed the power of rapid motion, generally 

 revolving round different axes, but sometimes progressive." 



Virgularia mirabilis is common in the east and north coasts of 

 Scotland ; it is found in the North Sea, and as far north as Norway. 

 In Zetland it is known as the sea-rush. It is abundant in Belfast 

 Lough, but, from its brittle nature, perfect specimens are difficult to 

 obtain. 



The genus Virgularia differs from that of Pennaiula chiefly in the 

 development of the axis of the colony and the shortness of the 

 pinnae, which carry the polyps ; and also in this, that no spicula enter 

 into the composition of its softer parts. 



" V. mirabilis seems," says Sowerby, " to represent a quill stripped 

 of its feathers. The base looks like a pen in this as in other species, 

 swelling a little way from the end, and then tapering. The upper 

 part is thicker, with alternate semicircular pectinated swellings, 

 larger towards the middle, tapering upwards, and terminating in a 

 thin bony substance, which passes through the whole extent, and is 

 from six to ten inches in length." 



Q 2 



