ORDER II 



FORAMINIFERA 



23 



The microspheric form is thus the result of a conjugation or sexual process, 

 while the megalospheric form is the result of simple division or an asexual 

 process. As a rule the megalospheric form is by far the most common, and 

 in many species the microspheric form is very rare, or even as yet unknown. 

 The microspheric form, while it Starts as a smaller individual, in most cases 

 attains a much larger size than the megalospheric, as might be suspected from 

 the nature of the reproductive processes by which it is formed. In species 

 where there are definite stages in development it is usually the microspheric 

 form which repeats these most fully, these stages being reduced or entirely 

 skipped in the megalospheric form of the species. 



In some cases the megalospheric form may give rise to a group of megalo- 

 spheric young instead of to zoospores. On the whole, the life cycle agrees well 

 with the alternation of generations as seen in certain other groups of animals. 









Fio. 6. 



Specimen of prepared White Clialk from Meudon, as seen in 

 transmitted light imder power of 300 diameters, showing Texhi- 

 laria, Globigerina, and Rotalia. 



Fio. 7. 



Thin slice of Plänerkalk from Bohemia, 

 viewed in transmitted light under power of 

 50 diameters, showing sections of Nodosaria, 

 Rotalia, Frondicularia, and numerous iso- 

 lated Globigerina Chambers. 



The vast majority of Foraminifera are marine in habit. They occur in 

 shallow water bordering the coasts, sometimes attached to algae, sometimes 

 creeping on the bottom. A few genera are extraordinarily abundant in the 

 open sea, being found at difFerent depths as free-swimming forms, and also on 

 the floor of the ocean. Enormous quantities of their remains are spread over 

 vast tracts of the sea-bottom, and down to a depth of 2300 fathoms they 

 remain an essential constituent of the deep-sea ooze. This is a finely divided 

 agglomeration of decomposed calcareous substances, such as the shells of 

 mollusks, corals, bryozoans, coccoliths, radiolarians, diatoms, sponges and 

 Foraminifera. Of the latter, certain genera are remarkable for their extra- 

 ordinary abundance (Globigerina, Orbulina, Pulvinulina, Biloculina) (Fig. 5). 



In the Atlantic and Pacific Oceans Globigerina ooze is the prevailing deep- 

 sea deposit; in the North Sea, along the coast of Norway, Biloculina ooze. 

 Numerous limestones and marls of older geological periods exhibit great 



