34 THE FOEAMINIFERA 



however, fundanientally different. All the chambers 

 in the Foraminifera are occupied by the sarcode, 

 whilst the cephalopod molluscs inhabit only the 

 last chamber, leaving behind them in the earlier 

 chambers merely a stolon or siphuncle. There is 

 also another difference between the two groups, for 

 while the septal face in the Nautilns is concave 

 anteriorly, that in the foramiiiiferal shell is generally 

 convex. 



All Foraminifera are not multilocular, for some 

 genera consist only of a single chamber at the most 

 advanced stage of growth, as, for example, the 

 chitinous form Groin ui, or the calcareous Larjena. 

 These were referred to as Monothalamia (single- 

 chambered) in Schultze's classification. 



The Shell Structuee. 



The shells ol the Foraminifera, although formed 

 by one of the simplest types of animal life, often 

 show (juite a complex structure. The outer shell- 

 wall is non-tubulate only in the group of the 

 Porcellanea or Imperforata ; but in all the sub- 

 divisions of the Foraminifera the septa dividing the 

 chambers are perforated by a tube or tubes called 

 stolon canals or passages (fig. 20), by which the 

 sarcode has free connnunication from chamber to 

 chamber, and which allows the passage of the nu- 

 cleus and other bodies contained within the proto- 

 plasm. These perforations of the septal walls are 

 identical with the oral apertures seen on the last 



