ORGANIC DEPENDENCE AND DISEASE 



89 



Fig. 73. The surface of a Stromatopora from whicli thi'ee individuals of Top- 

 sentia, a boring sponge, have been removed by weathering. 



been especially studied by E. Eay Lankester^ and W. C. 

 Mcintosh^ who have described the habits of such genera as 

 Sabella, Leucodore, Dodecaceria, whose individuals abun- 

 dantly penetrate corallines, corals, limestone and other 

 rocks, Sabella saxicava Quatrefages makes a usually 

 straight tube, but these are often deflected or curved, some- 

 times looped so that both extremities protrude. This loop 

 shape is a habit common to a number of worms which bury 

 themselves in soft mud, and is familiar in the sediments of 

 the Paleozoic rocks. Such U-shaped burrows into the sea 

 bottom have been recorded in rocks as old as the early Or- 

 dovician.^ The same shape characterizes some of the living 

 worms which construct agglutinated tubes. Such tubes as 



1 Annals and Mag. of Nat. Hist., April, 1868, p. 233, pi. 11. 



2 Ditto, October, 1868, p. 276, pi. 18, 20. See also W. Blaxland Benham in 

 Cambridge Natural History, 2, "Polychaet Worms," p. 287. 



3 See Hayes, op. cit. 



