W. H. HARRIS UN MARINE JIIC'ROSCOPIC VEGETABLE ORGANISMS. 151 



The former table refei.s to the porcellaneous dixisiou, in which 

 the vegetable organisms are scarce ; the latter to the hyaline 

 gi'oup, in which they are very well represented. 



Contrasting the two sets of tables, the chief difference appears 

 to be an excess of carbonate of magnesia, with a corresponding 

 diminution of carbonate of lime in the porcellaneous as compared 

 with the hyaline tests. 



Unequal Develo2ynient. 



Closely connected with the chemical constitution of organic 

 remains is the question of unequal development of individual 

 plants of the same species. Specimens collected from the same 

 dredging will vary considerably, not only in the size of the mature 

 plant, but in the diameter of the filaments. I fear that without 

 carrying out a close analysis of such fragments as present extreme 

 cases of development, no satisfactory conclusion can be arrived 

 at. By no means does it follow that, because the fragments are 

 contained in one dredging, they were built up under precisely 

 the same conditions. Currents will transport material enormous 

 distances ; and this opens the questions of depth, pressure, tem- 

 perature, and action of light, all probably exercising their influence 

 in different degrees upon the constituents of the organic remains. 



Starvation occurs in ocean depths, as well as on the land. 

 Permit me one quotation from Mr. Brady's Keport, page 131, on 

 this point : — '' In brackish water, where the supply of earthy 

 salts in solution is smaller than in the open sea, the chemical and 

 physical characters of the shells of such species as survive the 

 changed conditions are considerably modified. They become by 

 degrees less calcareous as the water grows less saline, until 

 eventually a point is reached at which the investment is little 

 more than a chitinous or horny membrane, strengthened by the 

 incorporation of minute silicious grains, but containing so little 

 carbonate of lime that it is scarcely altered by treatment with 

 acids. 



"A still more remarkable modification occurs in specimens 

 from the abyssal depths of the North Pacific explored by the 

 Challenger cruise. A few Miliolse, from soundings taken at a 

 depth of 3950 fathoms (about four miles and a half), scarcely 

 distinguishable in form from young thin-shelled specimens of a 

 common littoral species, were found to be unaffected by treatment 



