PROTOZOA. FORAMINIFERA. 17 



In the porcellanous and the lower vitreous forms 

 the septum between the chambers (fig. 1 A, b) is formed 

 entirely by the wall of the older chamber, but in the 

 higher vitreous forms each chamber possesses a wall of 

 its own, so that the septum (fig. 1 B, 6) is formed of two 

 lamellae. Also in the higher vitreous forms the walls of 

 the chambers are frequently strengthened by a deposit on 



A /? 



FIG. 1. A, section of a foraminifer in which each septum is formed of a 

 single lamella. B, in which the septum is formed of two lamellae, 

 a, passages between the chambers ; b, septum ; c, anterior wall of 

 last chamber; d, supplemental skeleton. (After Carpenter.) 



their outer surfaces, filling up the outer hollows between 

 the chambers ; this deposit is often traversed by a system of 

 canals, and is known as the supplemental skeleton (fig. 1 B, d). 

 The Foraminifera are divided into two sub-orders, 

 (1) the Imperforata, (2) the Perforata. 



SUB-ORDER 1. IMPERFORATA. 



The test is not perforated by canals, but is provided 

 with one or two large apertures, through which the whole 

 of the pseudopodia pass out. The test is membranous, 

 porcellanous, or arenaceous. 



w. p. 2 



