FORAMINIFERA 



345 



..-V-uv- 



Fig. 157. Diagram illustrating the life-cycle of Foraminifera (Kiihn). 

 a-c, microspheric generation; d, uninucleate phase; e-g, megalospheric 

 generation; h, isogametes; i-j, isogamy. 



thickness of shell varies considerably, as do also the size and 

 number of apertures, among different species. Frequently the 

 perforations are very small in the young and later become large 

 and coarse, while in others the reverse may be the case. 



The form of shell varies greatly. In some there is only one 

 chamber, composed of a central body and radiating arms which 

 represent the material collected around the pseudopodia, as in 

 Rhabdammina (Fig. 158, a), or of a tubular body alone, as in 

 Hyperammina (Fig. 158, d). The polythalamous forms possess 

 shells of various spirals. The first chamber is called the prolocu- 

 lum which may be formed either by the union of two swarmers or 



