Gait J ^f(l•ine Laboratori/, S(. Andrews. 305 



of the valves inwards, but such may he due to the facilities 

 art'orded by the numerous chinks and fissures between the 

 thin shelly plates tor the early operations of the aiineli Is of 

 this species, as pointed out by Dr. Carazzi. Po/ydora, more- 

 over, bores in univalves, not to allude to rocks and stones, 

 where the tubes could not be affected in this way. Nor will 

 the statement concerning the a|)pearances of the tubes, viz. 

 " becoming shallower inwards and ceasing to be grooved at 

 all," lend much support. The tubes end in a loop, which, in 

 shells that are worn, or when the loop occurs in a " blister " 

 or space, does not show the circular form (in section of the 

 shell) of the distal part of the tube. The circular form, how- 

 ever, is really kept up by the tunnel in the mud or by calca- 

 reous sediment in other circumstances, and both of which 

 may be washed away after death. The tube is thus con- 

 tinuous from one aperture to the other, and the annelid can 

 reverse itself therein, the head appearing at eitiier aperture. 

 The exact meaning of this part of the description is difficult 

 to comprehend. If it be that the proximal end or loop of 

 the tube indicates the site occupied by the postlarval worm 

 when it is "shut out" by the oyster, such, as already men- 

 tioned, does not accord with previous observations. 



Jt is also necessary to demur to the statement in the Report 

 that it is quite possible that in limestone and shale the annelid 

 " may take possession of a small depression, and as it grows 

 gradually enlarge it by its constant movements in and out, 

 until it has formed its tube in the same. Such tubes may 

 serve for a succession of generations, being still increased in 

 size by each occupant, as is the case with some of our sea- 

 urchins which form holes in the sandstone of Port Jackson. 

 But still there would be an absence of boring in the sense 

 used with reference to this worm." The supposition that the 

 swarm of finely-drilled tunnels on the free edge of a fractured 

 piece of limestone rock or the thick end of Chama have thus 

 been formed in fortuitous depressions cannot be accepted. 

 The surface of many of the rocks and stones drilled by 

 Folydora and Dodecaceria is perfectly smooth, and besides, 

 in not a few instances, the number and regularity of such 

 fortuitous depressions that would be necessary negative it. 

 The author's argument would be equally applicable to the 

 works of Teredo and Limnoria in timber, and would be 

 equally futile. Further, if oysters from certain Australian 

 beds be examined, tubes of Serpu/ce will be found in great 

 numbers on the surface, and some of these have been partially 

 enveloped by the shell during growth, so that they require 

 to be picked out. A careful examination of these tubes, for 



