152 W. H. HARRIS ON MARINE MICROSCOPIC VEGETABLE ORGANISMS. 



with acids ; and upon further examination it became apparent 

 that the normal calcareous shell had given place to a delicate, 

 homogeneous, silicious investment." 



The material I had from off Bird Island, Great Barrier Reef, 

 Queensland, was remarkable for the thinness of the tests of the 

 porcellaneous foraminifera and the fragments of the moUuscan 

 shells it contained, clearly indicating a struggle with the coral 

 for the mineral salts. It is therefore not unreasonable to assume 

 that under certain circumstances the animals may be deprived of 

 some portions of the constituents of their hard parts, and that 

 the effect of this is shown in the vegetable organisms by their 

 diminutive development; consequently I have been led to the 

 conclusion that measurements are to some extent valueless as a 

 means of identification of species. 



Distrihiit'wu. 



The geographical distribution of these organisms appears to 

 be world-wide. Wherever suitable material has been obtained 

 representatives of the group have been discovered. 



Some species appear to be cosmopolitan and plentiful ; others, 

 although widely distributed, are nevertheless more restricted to 

 particular areas, while others again may be comparatively local. 



The British coasts, if carefully worked, would, I believe, yield 

 a list equal to any area of similar extent in any part of the world. 



The table given on page 154 is a slight contribution to our 

 knowledge of the geographical distribution of the group. 



The bathymetrical distribution is probably influenced by tem- 

 perature. From the table given on page 155 it will be observed 

 that from the littoral down to 50 fathoms twenty-nine species 

 occur ; from this point to 450 fathoms the number is reduced to 

 nine species. 



According to the tables of ocean temperature in the Cludlenger 

 Reports, the greatest decrease takes place from the surface down 

 to 500 fathoms. From this point to the greatest depth the 

 decrease per 100 fathoms is considerably less. An extract from 

 the table St. Thomas to Bermuda will afibrd an illustration. The 

 surface temperature is given as 75 S'^; at 500 fathoms it is 45°, 

 a diminution of 30 '5°, or an average of 6*1° for each 100 fathoms. 

 The next 1,000 fathoms a diminution to olb^ takes place, or an 

 average of 0*75" per 100 fathoms. 



