112 



THE AUSTRALIAN MUSEQM MAGAZINE. 



cliambered heart aud a very fair iier- 

 70US system. It has no brain, though ; 

 the centre of the nervous system is a 

 thick nerve ring in the region of the 

 gullet. The larvae of the chiton arc 

 free swimming creatures, though the 

 adult animal cannot, of coui"se, swim at 

 all. 



MUSSELS. 



We now come to a bivalve or two- 

 shelled mollusc, the mussel, which you 

 will find on the lower rocks or around 

 the piles of wharves. The mussel is a 

 very near relation of the oyster, but it 

 is superior to the oyster in that the 

 adult animal has powers of locomotion; 

 the larval forms of both are free swim- 

 ming. The foot of the mussel, by which 

 it walks, is a most remarkable organ. 

 It is a continuation of the front part of 

 the body and is not unlike a tongue in 

 shape. It is thrust forward out of the 

 slightly open shell, and near the base of 

 the foot there is a gland which gives 



out a sticky, silky secretion, which har- 

 dens into a kind of thread when pro- 

 duced. The animal gets along by pro- 

 jecting its foot forward, fastening the 

 end of the thread produced from the 

 gland to some suitable spot, and then, 

 bringing back its foot suddenly, it pulls 

 on the thread and hauls itself along 

 through a fraction of an inch. Each 

 time it repeats this motion it fixes an 

 extra thread, and, when it has moved 

 sufficiently, this bimdle of threads, 

 known as the byssus, serves to anchor 

 it most securely to its support. The 

 byssus can be cast off if the mussel 

 wishes to move on at some future time. 

 THE (x;topus. 

 It seems rather curious to call the 

 octopus a shellfish, yet it really is a 

 mollusc and is related to the whelks, 

 periwinkles, and snails. But it has 

 carried its development so far that the 

 shell is a mere apology for a shell, a 

 rudiment only. It serves merely to con- 



Reef-building annelid worm (Galeolaria canspitosa). 



White masses of annelid iworm tubes cover the rocks from about tlie 

 mid-tide zone to the limit of the neap tides. In the quieter waters 

 they thickly encrust the rocks and wharf piles, presenting the appear- 

 ance of coral, but are less abundant on the open coast where adverse 

 conditions apparently restrict their growth. 



Plioto. — A. Musgrave. 



