r. M. yongp: 



tissues from them. When a branch of this genus is decalcified and 

 the polyp layer carefully stripped off, either of these boring organ- 

 isms will be seen to have formed a close-meshed network, showing 

 accurately the shape of the original branch with all its twigs." Gar- 

 diner considered that neither of these organisms bores into anything 

 but newly secreted coral skeletons. As noted above, thev could pro- 

 vide food for boring sipunculids and, less probablv, polvchaetes. The 

 different, much more finely ramifying, type of growth within coral as 

 compared with bivalve skeletons mav well be related to differences 

 in the skeleton, possibly in the organic content. Goreau and Hart- 

 man add greatly to our knowledge of the boring of sponges into 

 corals in their contribution to this symposium (chapter 2). 



PoLYCHAETES. The bcst-kuown polvchaete rock borers, always 

 apparently boring into calcareous substrates, are species of Polijdora, 

 which may be serious pests of oysters in many parts of the world. 

 These small worms initially form mucous tubes to which mud ad- 

 heres. They tend to back into crevices and can then bore if the sub- 

 strate is suitable. They do so with the bodv bent double into a U, 

 the arms of which are separated by a partition of mud and debris 

 consolidated in mucus. Boring must be in part, if not wholly, me- 

 chanical, possibly bv the agencv of enlarged dorsal setae on the 

 fifth setigerous segment. Since the substrate is apparently always 

 calcareous, boring could be assisted by some initial chemical action, 

 although there is no evidence of anv glands on the surface of the 

 body. Other species inhabit crevices in shale and sandstone. There 

 seems to be some doubt as to whether these ever bore; if not, it 

 could be because the rock is harder, not because it is noncalcareous. 



CiRRiPEDES. The attached habit of barnacles has led, following 

 fixation to the body of animals, to various degrees of commensalism 

 culminating in parasitism. It has also, most notablv in the genus 

 Lithotrya, led to penetration of the rock on which the c\'pris larvae 

 settle. Species of this genus are among the commonest borers on 

 both Indo-Pacific and Atlantic coral reefs (Cannon, 1935; Seymour 

 Sewell, 1926). The chitinous covering of the contractile peduncle 

 contains numerous "nail-like bodies, the head of each nail being 



