279 



folium of the Mississippi is supposed by fishermen to feed 

 upon the mud and slime at the bottom of the river, but is 

 found to consume an enormous amount of entomostraca, 

 while fully one-fourth of its food is composed of vegetable 

 algae, which are obtained by means of its long and double 

 row of fine gilt rakers, forming a strainer, which permits the 

 passage of the fine silt of the river, but arrests everything 

 else as large as a cyclops. In the New South Wales 

 section of this Exhibition may be seen the teeth in the jaws 

 of a shark, Heterodontus galeatus, stained of a pinkish 

 purple, due to its feeding largely on an Echinoderm common 

 in Port Jackson, the Centrostephanos rodgersii, which stains 

 them of that colour. This tempting morsel has spines 

 about three inches long, and must be a very prickly subject to 

 swallow. The spines of other Echinoderms, Amplypneustes 

 ovem and Strongylocentrotus erytherogrammus have also 

 been found in the intestinal tract of this fish. The torpedo, 

 or cramp fish, paralyses its victim. 



The colours of fish may be dependent upon the food on 

 which they subsist ; thus Professor Mobius found in the 

 stomach of some cod large pieces of two marine plants, 

 ULva lactaca and Zostera marina, irrespective of shells, 

 snails, crabs, and fishes. These had affected the external 

 colour of the cod, and thus became indicative of the depths 

 at which they live ; these variations comprised white, yel- 

 lowish brown, speckled, green, and black. The same 

 change of colour, induced by alterations in food, has been 

 observed at Sir James Gibson Maitland's trout ponds at 

 Howietown, near Stirling. 



Some fishes feed at night-time, others during the day ; 

 while what is eaten when in captivity is not invariably a 

 criterion of what they consume when in a state of nature. 

 Thus in Ireland cod fish and haddock kept in vivaria have 



