FORAMINIFERA 



193 



some species of Miliolidae inhabiting either the brackish water 

 of deep sea. Calcareous tests are sometimes imperforated, but 

 even in such cases those of the young are always perforated. By 

 far the majority of the Foraminifera possess perforated cal- 

 careous tests. The thickness varies considerably, as do also the 



a V 



Fig. 73 Diagram showing the development of Foraminifera. (After Kiihn). 

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

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



size and number of apertures, among different species. Fre- 

 quently the perforations are very small in the young and later 

 become large and coarse, while in others the reverse may be the 

 case. 



