ZOOLOGY 



SECT. 



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

 terminal aperture, pseudopods are protruded (Fig. 34, #). 



In many cases additional complexity is attained by the develop- 

 ment of what is called the supplemental skeleton (Fig. 35, Sb, s. sk.). 

 This consists of a deposit of calcium carbonate outside the original 

 shell : it is traversed by a complex system of canals, containing 

 protoplasm, and is sometimes produced into large spines. 

 Foraminifera in which this secondary skeleton occurs are some- 

 times of considerable size 2-3 cm. in diameter and of extra- 

 ordinary complexity. 



Many Foraminifera resemble Difflugia in having a skeleton 

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

 cemented together by a secretion from the protoplasm (Fig. 35, 1). 

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



sfi 



FIG. 36. Hastigerina murrayi. plsrn. vacuolated protoplasm surrounding shell : psd. 

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



protoplasm protruded from a single terminal aperture ; others on 

 the perforate type, small pseudopods being protruded between the 

 particles forming the shell. 



In many cases the pseudopods are the only portions of proto- 

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

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

 an internal structure. In one of the calcareous forms with 

 perforated spiral shell, called Hastigerina (Fig. 36), a very remark- 

 able modification of this condition of things obtains. The shell 

 (sh.) is surrounded with a mass of protoplasm (plsm.) many times 

 its own diameter, and so full of vacuoles as to present a bubbly or 

 frothy appearance. The shell itself, moreover, in this and allied 



