RHIZOPODA. 1 1 



Paris basin, which makes an excellent building stone, contains the 

 Triloculina trigonula (Miliolite chalk). 



The greater number of Foraminifera are marine, and move by 

 creeping on the bottom of the sea, but some of them are pefagic and 

 Globigerina and Orbulina live at the surface. Some of the genera 

 are found in the brackish water of estuaries, and they may even 

 extend into fresh water. The bottom of the sea at very consider- 

 able depths is also covered with a rich abundance of forms, 

 especially with Globigerina, the remains of the shells of which give 

 rise to an enduring deposit. 



Order I. Amoeboidea. 



Naked Amoeba-like Rhizopoda, with lobose or reticulate pseudo- 

 podia, usually with nucleus and contractile vacuole. 



Amceba, nucleated forms, with contractile vacuole and lobose pseudopodia. 

 Protamasba Haeckel, small forms, with lobose pseudopodia ; nucleus and con- 

 tractile vacuole not observed. Hyalodiscus Hertwig and Lesser, disc-shaped, 

 nucleated forms, without pseudopodia ; locomotion by a flowing movement 

 without change of form. Protomyxa Haeckel, Myxodictyum Haeckel, Protogenes 

 Haeckel, are forms with anastomosing pseudopodia, and without observed nucleus. 

 PelomyxaGreef, large amceba-like forms, containing many nuclei, refractile bodies, 

 and cylindrical crystals. Other genera are Gloidium Sorokin, Chcetoproteus Stein, 

 Plakopus F. E. Schulze, Dactijlosphcsra Hertw. and Lesser, Podostoma Clap, and 

 Lachm., Amphizonclla Greef, Gymnophrys Cienk. Baihybius Huxley, found in 

 the deep sea mud of the Atlantic, if it is indeed a living organism (and not 

 simply a deposit of gypsum). Coccoliths, Coccospheres, and Rhabdospheres are 

 found in the gelatinous mud of the bottom of the Atlantic, and were supposed 

 by Huxley* to be portions of the body of Bathybius. Similar bodies have been 

 found in the chalk. They are in reality small marine vegetable organisms, with 

 calcareous walls, and are oceanic in habit. They form with Diatoms and pelagic 

 Oscillatorice, a large part of the vegetable food of marine animals, f 



Order II. Testacea (Foraminifera). 



Principally marine Rhizopods, with a shell which is either 

 membranous, calcareous, or rarely silicious, and may be single- 

 chambered (Monothalamia) or many-chambered (Polythalamia), 

 usually with more than one nucleus. 



In this order the pseudopodia are generally slender and 

 anastomosing, but in the fresh water Arcella and Difflugia (Fig. 8) 

 they are lobed. The protoplasm has the power of exuding through the 

 openings in the shell and of forming a layer which may be much 

 vacuolated on the outside of the shell (Fig. 10). In such cases the 

 shell may be regarded as an internal structure, and appropriately 



* Q.J.M.S., vol. 8. f Vide Nature, 1897, p. 510. 



