54 PROCEEDINGS OF THE 



all the pieces of shells with which it is overlaid being j^laced along 

 the inner frame of the tube in pentangular rows. 



No 10, Nothria conchjlega (Sars), is less symmetrical, the tube 

 being greatly depressed and rugged at the edges, with a coarse 

 and irregular aspect; but when we examine it with care we see 

 a strict application of means towards an end. It will be observed 

 that all the building materials (fragments of shells) have been 

 laid down in the under row with the concave side up, and in 

 the upper row with the concave side down, thereby forming a 

 flat tube for the lodgement of the animal. It will be noticed that 

 the pieces with which it is built are mostly of a considerable size, 

 and so laid as to secure the greatest possible strength, which is 

 accomplished by laying one piece over the other in such a way 

 that an upper piece will cover the joining of two under pieces, a 

 process familiarly known to builders by the name of "breaking 

 band." This again anticipates one of the universal principles 

 both of ancient and modern architecture. 



There are many tube builders v/hose materials are laid less 

 orderly, and where the cement is more gelatinous and yielding in 

 character than in the cases we have noted, as in Nos. 11, Lanice 

 conchilcga (Pallas), and 12, Thehims circiniiatus (Fabricius). There 

 are others, as No. 13, also Lanice, where the fine sand forming the 

 tube is held together by a very thin mucous secretion of the animal. 

 These tubes are often very long; some that have come under 

 my own observation being formed in the following way: — The 

 animal gathered a ring of sand round its neck, where it was 

 supplied with the requisite amount of mucus to secure cohesion; 

 from thence the ring was carried down to the posterior end of the 

 body. Other rings were formed, and followed each other in the 

 same way till the tube was completed. 



Some species of these annelids are solitary, while others arc 

 gregarious. On the south-east side of Luce Bay the interstices of 

 the shingle between tide-marks are closely filled up with the 

 arenaceous cases of a colony of Sabellaria alveolata, in some places 

 fringing the sides of pools, and at other points covering the 

 flat rocks with a solid crust. It may be remarked that this 

 annelid is not always gregarious, nor in all cases confined to the 

 tidal belt, as I have often brought it up in the dredge at Cumbrae 

 in twos and throes adhering to the valves of Pcdcn oj^crcidaris, 

 from a depth of twenty-five fatlioms. 



