ZOOLOOY SECT. 



rface, a corresponding thickness being, probably, removed by 

 ution from the inner side at the same time. 

 The shell presents two leading types of structure apart from 

 3 form and arrangement of the chambers : either it is of a 

 rcelain-like texture and provided with a single terminal apertui'e, 

 ig. 35, 4), or the texture is glassy and the whole shell perforated 

 th very minute apertures, through which, as well as through the 

 •minal aperture, pseudopods are protruded (Fig. 35, 2). 

 In many cases additional complexity is attained by the develop- 

 !nt of what is called the siopplemental skeleton (Fig. 36, 8h, s. sh.). 

 is consists of a deposit of calcium carbonate outside the original 

 5II; it is traversed by a complex system of canals containing pro- 

 )lasm, and is sometimes produced into large spines. Foraminifera 



fisa 



S7. — Hastigerina murrayi. pUm. -vacuolated protoplasm surrounding shell: psd. 

 paeudopods ; sh. shell ; sp. spines. (After Brady.) 



which this secondary skeleton occurs are sometimes of consider- 

 e size — 2-3 cm. in diameter — and of extraordinary complexity. 

 Many Foraminifera resemble DifHugia in having a skeleton 

 med of sand-grains, sponge-spicules, and other foreign bodies 

 nented together by a secretion from the protoplasm (Fig. 36, 1). 

 me of these are formed on the imperforate type, having the 

 )toplasm protruded from a single terminal aperture ; others on 

 i perforate type, small pseudopods being protruded between the 

 •tides forming the shell. 



[n many cases the pseudopods are the only portions of proto- 



,sm outside the shell, whereas in Gromia, as we saw, the shell 



invested with a layer of protoplasm, and is thus in strictness 



internal structure. In one of the calcareous forms with 



