THE DAWN- ANIMAL AS A TEACHER IN SCIENCE. 221 



for this. But whatever the cause, it is usual to find 

 fossil Foraminifera with their sarcode replaced by 

 such material. We also find beds of glauconite re- 

 taining the forms of Foraminifera, while the calcareous 

 tests of these have been removed, apparently by acid 

 waters. 



One consideration which, though conjectural, de- 

 serves notice, is connected with the food of these 

 humble animals. They are known to feed to a large 

 extent on minute plants, the Diatoms, and other 

 organisms having silica in their skeletons or cell- 

 walls, and consequently soluble silicates in their juices. 

 The silicious matter contained in these -organisms is 

 not wanted by the Foraminifera for their own 

 skeletons, and will therefore be voided by them as 

 an excrementitious matter. In this way, where 

 Foraminifera greatly abound, there may be a large 

 production of soluble silica and silicates, in a condition 

 ready to enter into new and insoluble compounds, and 

 to fill the cavities and pores of dead shells. Thus 

 glauconite and even serpentine may, in a certain 

 sense, be a sort of foraminiferal coprolitic matter or 

 excrement. Of course it is not necessary to suppose 

 that this is the only source of such materials. They 

 may be formed in other ways ; but I suggest this as at 

 least a possible link of connection. 



Whether or not the conjecture last mentioned has 

 any validity, there is another and most curious bond 

 of connection between oceanic Protozoa and silicious 

 deposits. Professor Wyville Thompson reports from 



