40 



"genns by j^arallel granular bands, regarded as muscu- 

 "lar libers by some writers. The usual food-balls and 

 ••vacuoles are present, and I was enabled to define 

 ••sliarply tlie endosarc from the ectosarc, and clearly 

 "see the long, beaded nucleus. The tube or ribbon- 

 " secreting organ described by AVright I Avas unable to 

 "discover. 



•• AVhen fully extended tlie basal j)ortion of the animal 

 •'becomes attenuated to a thin bluish hlament, Avhich 

 •'widens towards the peristome, where the body is over 

 • ' half as thick as the inside diameter of the tube. AVhen 

 ••fully retracted and resting, the animal resembles in its 

 ••oblong shai^e a retracted and resting Steiitoi\ and meas- 

 "ures about 1-10 as long as when fulh^ extended. The 

 "ribbon which forms the tube makes from four to twenty- 

 " four turns in specimens of different ages." 



THE F:\rX.E OF OYSTEK BEDS AS IXTEKDEPEXDEX^T COM- 

 MUNITIES. 



Mobius calls an oyster bank a Biocoenosis or interde- 

 pendent community of life. The many species of animals 

 found on the banks and beds are no doubt more or less 

 mutually dependent upon each other for subsistence, but 

 this is perhaps not any more true of oyster banks than it 

 is of terrestrial faun^. There are no doubt vast numbers 

 of floating embryos of oysters eaten by other animals 

 growing on the beds which bring their food supply to 

 themselves by means of currents produced by ciliary mo- 

 tion. On the other hand there are no doubt vast num]~)ers 

 of the minute swimming em]:>ryos of these, drawn in and 

 swallowed by the oyster, which may indeed, for aught we 

 know, i]i this way swallow many of its own young, for the 

 current produced by the oyster by means of the cilia 

 clothing its gills is by no means a feeble one. though it is 

 exceeded in poAver by the current flowing into and out of 

 the siphons of Jlya. In the latter I have frequently, upon 

 opening tlie animal, found several Copepeda plainly vis- 

 ible to the naked eye swimming about in the water in the 



