With the exception of the Balani (Acorn-Barnacles), perhaps the most common objects to be met with at the sea-shore are the SerpulÆ. Scarcely a rock, or shell, or bit of old china, or piece of wood, or rusty nail, lying near low-water mark, but is encrusted with colonies of these animals. I have a small twig of a tree by me, so thickly coated with SerpulÆ as to obscure all signs of its ligneous character, except at each end. A shell also exhibits the same phenomenon, and well-nigh defies the most skilful observer to define its original form with any degree of certainty.

The shelly tubes of these animals are built in the form of serpents, or twisted funnels, of a milk-white colour. Although so extremely hard, these tubes are formed solely by an exudation from the body of the animal—a simple marine worm. Unlike its erratic friend, the earth-worm, the Serpula is sedentary in its habits, and at no time does it ever leave its dwelling.

The delicate, but brilliant feathery plume—the only portion of the animal ever visible—constitutes the principal mechanism by means of which the Serpula constructs its calcareous tube.

A most wonderful instance of how mighty are the works which these insignificant creatures form when congregated together in vast numbers, and how useful such labours may sometimes be to mankind, is narrated by Dr. Darwin in his 'Voyage of the Beagle.'

Being delayed by adverse winds, this gentleman made a stay at Pernambuco, a large city on the coast of Brazil, and the most curious object that he saw there was the reef that formed the harbour. 'I doubt,' to use his own words, 'whether in the whole world any other natural structure has so artificial an appearance. It runs for a length of several miles in an absolutely straight line, and parallel to, and not far distant from the shore. It varies in width from thirty to sixty yards, and its surface is level and smooth; it is composed of obscurely stratified hard sandstone. At high water the waves break over it; at low water its summit is left dry, and it might then be mistaken for a breakwater erected by Cyclopean workmen. On this coast the currents of the sea tend to throw up in front of the land long spits and bars of loose sand, and on one of these the town of Pernambuco stands. In former times a long spit of this nature seems to have become consolidated by the percolation of calcareous matter, and afterwards to have been gradually upheaved, the outer and loose parts during the process having been worn away by the action of the sea, and the solid nucleus left as we now see it. Although night and day the waves of the open Atlantic, turbid with sediment, are driven against the steep outside edges of this wall of stone, yet the oldest pilots know of no tradition of any change in its appearance. This durability is by far the most curious fact in its history; it is due to a tough layer, a few inches thick, of calcareous matter, wholly formed by the successive growth and death of the small shells of SerpulÆ, together with some few Barnacles, &c. These insignificant organic beings, especially the SerpulÆ, have done good service to the people of Pernambuco, for without their protective aid the bar of sandstone would inevitably have been long ago worn away, and without the bar there would have been no harbour,'

Nothing whatever appears to be known relative to the mode of reproduction of these Annelids. I have paid much attention to the subject, but as yet have not gained any positive information regarding it. The only fact which I consider worthy of being chronicled is the following: On one occasion, when quite a novice in Marine Zoology, while observing a beautiful group of SerpulÆ seated on a stone, I saw issuing from out one of the tubes a kind of very fine dust, of a rich crimson hue, which continued to arise for nearly an hour in spite of repeated efforts to disperse it by aid of a camel-hair pencil. At first I believed the 'dust' to be the 'remains' of a deceased serpula, but afterwards found that such was not the case, the annelid being alive and healthy. Never having seen the phenomenon since, it has been a great source of regret to me that I did not endeavour to discover what the dust was composed of; but have little doubt that the microscope would have shown it to be, in reality, the ova of the Serpula.

Another class of Annelidans, termed SabellÆ, like the SerpulÆ, also build habitations for themselves, but not of the same materials. Instead of being white, the tubes of the first mentioned animals are brown in colour, and composed of minute granules of sand, or small shells, and lined internally with a gelatinous substance exuded from the body of the worm. On the interior of the oyster and other shells, and even in univalves occupied by the Lobster Crab, various tubes of SabellÆ may often be seen. They are, however, generally discovered congregated together, forming a kind of honeycomb mass in the fissures of rocks, or against the sides of rock-pools, or on the surface of small stones, &c.

A mass of SabellÆ tubes forms by no means an inappropriate or unpleasant object for the tank, as the animals are hardy, and will live for many months if the water be kept pure. Moreover, while in confinement, they do not live in luxurious indolence, but ever seem to be busy in the exercise of their architectural propensities, making alterations, repairing damages, or otherwise 'sorting' their tubiculous habitations.

'The tubes of the SabellÆ,' says Dr. Williams, 'are soft, flexible, and muddy. Slimy mucus furnished by the integumentary glands of the body is the mortar or cement, fine sand molecules are the "stones" or solid material of the architecture. In the SabellÆ the lime of which the tubes are built is held in solution in the mucus provided by the cutaneous glands. It is adjusted in the fluid form, and moulded by appropriate tools into the required shape. It then solidifies, too, under water, like the "Aberthaw lime." The tube of the SabellÆ fits closely round the body of the worm; it is slightly elastic, and the interior is smooth.'