ORGANIC DEPENDENCE AND DISEASE 
89 
Fig. 73. The surface of a Stromatopora from which three individuals of Top- 
sent.ia, a boring sponge, have been removed by weathering. 
been especially studied by E. Ray Lankester 1 and W. C. 
McIntosh 2 who have described the habits of sncli 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-sliaped burrows into the sea 
bottom have been recorded in rocks as old as the early Or- 
dovician . 3 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,’ 7 p. 287. 
s See Hayes, op. cit. 
