Homes or Tubes formed hy Annelids. ' 17 



Those Serpulids witli angular tubes of great density, and 

 firmly fixed to shells and stones, are represented by Pomato- 

 cerus with its ridged tube and bold sharp oral spine, and by 

 the viti'eous home of Placoslegus. The former often occurs 

 in great numbers (as in Lochmaddy) under stones and on 

 rocks between tide-marks, wiiile the latter frequents deep 

 water. The accuracy with which the pattern of each tube is 

 preserved in every example is noteworthy, just as each species 

 of niollusk secretes its special shell. This is the more evident 

 in the shelly tubes dredged by the ' Challenger,' in which the 

 patterns on the surface are complex. Such, for instance, is 

 the transversely ribbed Placostegus ornatus from 2900 fathoms 

 in the depths of the Pacific, and the pentagonal tube of 

 Placostegus henthalianus from the middle of the same ocean 

 at 3125 fathoms. In the latter the three upper ridges are 

 prominent and armed with blunt teeth. Lastly, the dense 

 tube of Placostegus Morchii has a deep groove on each side, 

 and comes from the Pacific, at 2373 fathoms, midway between 

 Sydney and Valparaiso. 



Other examples of shelly tubes are seen in the little coils 

 of Sj)irorbis, which stud the blades of seaweeds, the backs of 

 crabs, and other marine structures. 



All the foregoing are fixed, or, if free, form agglutinated 

 masses ; whereas another form {Ditrypa) secretes a hard, 

 smooth, calcareous tube, tapered and distinctly curved, which 

 remains quite free in the mud, muddy sand, or shell-gravel. 

 It resembles the elephant's-tusk shell (the home of a mollusk), 

 but is the product of an annelid closely allied to Serpula. 



Such, then, is a brief outline of a few of the interesting 

 types of " homes " formed by marine annelids. Slight as 

 the sketch has been it nevertheless will be apparent that 

 the amount of skill and perseverance in the construction of 

 these dwellings can hardly be surpassed by any other group 

 of animals — whether marine, freshwater, or land. No basket- 

 insects' work is more ingenious, and even the combs of the 

 bees and wasps and the nests of the most skilful birds are 

 not more complex examples of workmanship than the tube of 

 Amphictene or than that of Terehella with its terminal fringes. 

 Their work is more marvellous than any home formed by 

 fishes, which generally seek hollow seaweeds, holes in rocks 

 or similar places ; and the comparatively rough nests of the 

 fifteen-spined sticklebacks of the tidal rocks, or those of the 

 common sticklebacks of freshwaters, are not to be compared 

 with the wonderful architecture of the annelids. Even man, 



Ahu. S: Mag. X. Hist. Ser. 6. Vol. xiii. 2 



