304 Prof. M'lntosh's Xotes from the 



tlie University in 18S3 by tlie Trustees of the Australian 

 Museum. It might have been supposed that the margin of the 

 mantle ^voulcl have affected the intruding body by a calcareous 

 secretion. 



]\Ir. "VVhitelegge gives three figures (6, 7, and 8, pi. iv.) of 

 sections through the tubes of Pohjilora, viz. 7, a single tube 

 (loop at inner end), which he supposes is the first stage in 

 which the worm rests on the flattened solid part of shell, and 

 over wliich (the quiescent worm) the oyster forms a layer, 

 semicircular in transverse section. In the next stage (tig. 8) 

 the semicircle has become a keyhole, namely, there is a 

 tendency to a double tube; whilst in the third stage (fig. 9) 

 the two tubes are distinctly separated. But the same appear- 

 ances are found in the borings of the annelids in limestone- 

 rock, chalk, and shale, and are not related to the secretions of 

 the oyster. His first stage is the loop at the end of the 

 tunnel, his second is the commencement of the double tube in 

 an instance where the loop has been very short, whilst his 

 third stage is the distal portion of each tunnel. The latter is 

 a simple circular tube with a loop internally. Tiie appear- 

 ances figured, therefore, represent certain parts of the tunnel, 

 but the interj)retation of their formation differs. 



The whole position taken up by the author is lost at the 

 foot ot page 8 of the Report, where, after mentioning the 

 entrance of the worm " into the open shell," the collection of 

 mud, and the investment by the layer of shell (how it 

 manages to live alter this encystmeut is not explained), he 

 adds, " the body of the worm, resting on the shell, has by 

 reason of the constant movements in and out a tendency to 

 wear away the shell"; ''whether this is accomplished by 

 strictly mechanical means or by a corrosive acid 1 am unable 

 to say, but the fact remains that it is worn away." There is 

 no doubt the repoiter would have arrived sooner at this con- 

 clusion if, instead of confining his observations to oysters, 

 esj)ecially those having the " blisters " internally, he had 

 studied the action of tlie worm on limestone and on shale. 

 The observations were evidently made with much care and 

 display great acuteness ; but it is difficult at first sight to 

 giasp all the circumstances affecting these complex processes. 

 Again, the opinion is expressed that when the worm has 

 been long in the shell the " grooves " are deep, and the 

 longer they remain the deeper they become, from the fact 

 that " the growth or increase in tlie size of the shell forces 

 the entrances further outward and upwards or downwards, as 

 the case may be, according to whether it is the upper or lower 

 valve." It is true many of the tunnels pass from the margin 



