6 FORAMINIFERA 



The microspheric form is thus the result of a conjugation or 

 a sexual process, while the megalospheric form is the result of 

 simple division or an asexual process. As a rule the megalo- 

 spheric form is by far the more 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 more 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 megalospheric 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. 



The relations of the microspheric and megalospheric forms to 

 an understanding of the development of the group will be dis- 

 cussed later. 



Habits 



Most foraminifera are bottom-living forms, crawling slowly 

 about on the surface of the ocean bottom muds and oozes, or at- 

 tached to various objects on the ocean bottom. All foraminifera 

 are free in their earliest stages. There are numerous fixed 

 forms such as Carpenteria, Rupertia, Homotrema and others 

 which become fixed in the early stages and thereafter do not 

 again become free. There are many more forms which may at- 

 tach themselves loosely to other objects for all or a part of their 

 life history, but are never fixed. Hydroid stems are often en- 

 crusted with a mass of living foraminifera of the Rotaliidae and 

 Miliolidae. The short eel grass, Posidonia, of tropical shallow 

 waters is often covered with specimens of Planorbulina, Sorites, 

 and other forms. These may later detach themselves and be- 

 come free. A few species have become adapted to a pelagic ex- 

 istence and their modifications will be discussed on a later page. 



The rate of movement in the foraminifera is very slow, yet 

 when compared with their size, they may cover considerable dis- 

 tances. In order to pick up material for the test in those species 



