4 FORAMINIFERA 



when these are known in detail, they become of importance in 

 determining the age of sediments and the conditions under 

 which they were deposited. 



In spite of the fact that so much has been written in regard to 

 the foraminifera, a literature now including several thousand 

 papers, very little has been written about the animal itself. This 

 is surprising when they may be obtained on almost any seacoast 

 and may live and develop for years in a balanced aquarium. 

 Until only in very recent years has the complete life history been 

 known. Much remains to be done on the habits and the physio- 

 logic characters of the animal in the different groups. Such 

 studies will probably add materially to our knowledge of rela- 

 tionships in the group. 



The animal in the foraminifera should be considered as living 

 both inside and outside of its test. In other words the test in 

 many groups at least is an internal one. Even in the imperfor- 

 ate groups the ornamentation of the exterior is added to after 

 the test is completed, and in such forms even when disturbed, 

 the protoplasm is not wholly withdrawn into the test. 



The living animal consists of a mass of protoplasm with a 

 nucleus, the latter inside the test while the thinner protoplasm 

 streams out from the test in fine reticulate pseudopodia in all 

 directions. In these streams, there are usually two currents, the 

 central portion moving outward, and the periphery moving in- 

 ward toward the test. This is not a steady movement but has 

 definite rhythms. The form of the pseudopodia in the different 

 families is not the same, and these should be further studied. 

 The incoming currents bear food particles and debris of various 

 sorts thus in attached specimens, the outer surface often be- 

 comes more or less covered with such debris. The pseudopodia 

 in the moving or feeding individual often extend out very many 

 times the diameter of the test. The whole animal in the free 

 forms may move forward with its test over the surface at a slow 

 pace. 



It may be rather definitely stated that individuals of different 

 species at least, are repellant to one another. Numerous exam- 

 ples of this were observed at the Tortugas laboratory. There is 

 certainly no fusing of individuals of different species or genera 

 to form tests of an intermediate character as has been some- 

 times advanced in theory. 



