SABELLARIA. 249 



perhaps the variety of the architects, which has never heen the sub- 

 ject of sufficient observation. Thus we find the fabric, when a cyhn- 

 drical segment running over some flattened surface, firm, durable, 

 and capable of great resistance. It is not easily crushed. On the 

 other hand, when cylindrical or alveolar, it appears to be always 

 more brittle. Most of the dwellings of the Sabella are lined with a 

 fine silky substance formed of an exudation escaping from the body, 

 which, consisting of indurated glutinous matter, is very conspicuous 

 on breaking up the alveolar mass of some old congeries. The ani- 

 mals testify a decided preference on choosing the materials of their 

 habitations. While always preferring sand and comminuted shell, 

 pounded glass is sparingly and reluctantly employed, and unless for 

 a few fragments, it is soon entirely rejected. 



"But there is a striking difference in the character of the tubes. 

 One is short and confined, extending little beyond mere accommoda- 

 tion for the body ; another is considerably prolonged, so as to afford 

 a safe retreat in times of danger. The architect of a third seems to 

 persist in advancing the fabric as long as it can procure materials. 

 It never wearies of working*." — ** Night is the chief season of archi- 

 tectural labour, though perfect idleness never leaves the day unoc- 

 cupied. By means of the tentacular organs, and the cleft in the 

 anterior part, grains of sand are selected and adapted to the precise 

 spot, where glutinous matter secures them to the tube for sheltering 

 its otherwise defenceless tenant." 



This tenant is wonderfully made. The body is less than an inch 

 in length, of a subquadrangular form, slightly tapered from the 

 thorax to the tail, which is terminated with a narrow caudal append- 

 age, usually curved or bent upon the back : the anterior portion is 

 generally coloured with purple ; the abdominal is straw-yellow, 

 becoming pink or fine red posteriorly. The head is in the form of 

 a circular opercular disk divided into two equal halves by a slit, and 

 consists of three concentric rows of bristles which have a pearl-like 

 polish, and are very remarkable in their disposition and structure. 

 In the centre of the disk we find the mouth in the form of an ellip- 

 tical fissure surrounded with the inner row of bristles inclined towards 

 the orifice. These bristles are triangulate, the portion imbedded in 

 the parenchyma being elongate, narrow, and cylindrical, while the 

 exposed portion is suddenly altered in direction so as to make a knee 

 at the bend, whence it tapers gradually to a point. This portion is 

 brown, and finely striated crosswise (No. XLIII. fig. 1). The middle 

 circle consists of bristles which have a large bulged subtriangulate head, 

 supported on a narrow stalk, entirely immersed in the flesh (fig. 2) . 

 The head is brown, hollow, beautifully striated crosswise, and ciliated 

 on the edges of the opening in front. The bristles of the marginal 

 circle look outwards, and form a denticulated fringe. Each bristle 

 resembles a fork, with from five to seven unequal prongs (fig. 3). 

 The shaft is narrow, elongated, with a sharp point, expanding above 

 into a broad flattened hand, divided at the apex into sharp unequal 



* On the contrary, De Quatrefages could not get his specimens to work at all. 

 —p. 27. 



