PROTOZOA: FORAMINIFERA. 51 



lieved to constitute a genuine structural distinction, and the 

 Foraminifera may be thereby divided into two great groups 

 (Perforata and Imperforata). 



As regards the soft parts of the Foraminifera^ the body is 

 composed of extensile and contractile sarcode usually red- 

 dish or yellowish in colour which not only fills the interior of 

 the shell, but generally invests its outer surface also with a thin 

 film, from which the pseudopodia are emitted. The test, there- 

 fore, in this case, is not a true cuticular secretion, like that of 

 the Mollusca, but it is truly immersed within the sarcode of the 

 body. The sarcode is not differentiated into a distinct ectosarc 

 and endosarc, and is devoid of a nucleus and contractile 

 vesicle, and, indeed, of any organs or specialised parts of any 

 kind. From this uniformity in its composition there seems 

 some reason to conclude that the Foraminifera in spite of the 

 complexity and mathematical regularity of many of their shells 

 should be looked upon as the lowest forms of the Rhizopoda, 

 or even of the Protozoa. 



The pseudopodia in all the Foraminifera (fig. 4, , c) are fila- 

 mentous and protrusible to a great length, and they possess the 

 singular property of uniting together in various directions so 

 as to form a kind of network, like an "animated spider's 

 web." (Hence the name Reticulosa applied to the order by 

 Dr Carpenter.) This property, however, is not peculiar to 

 members of this order, but is seen also in Actinophrys and in 

 the Thalassicollida, though to a less extent. Further, through- 

 out the entire network formed by the inosculating pseudo- 

 podia there is a constant circulation of granules in different 

 directions. This singular phenomenon is in many respects 

 analogous to the Circulation of granules which is seen in 

 many vegetable cells, and it is believed by Dr Carpenter that 

 " the conditions of the two sets of phenomena are essentially 

 the same." 



The shells of Foraminifera may be classed in three divisions, 

 termed respectively the " porcellanous," the " hyaline " or 

 " vitreous," and the " arenaceous." The porcellanous shell is 

 quite homogeneous in its composition, is opaque-white when 

 seen by reflected light, and is not perforated by pseudopodial 

 foramina. In these forms (e.g., Miliola, fig. 4, b] the pseudo- 

 podia are emitted solely from the mouth of the last-formed 

 segment of the shell. The vitreous shell is transparent and 

 glassy in texture, and its walls are perforated by numerous 

 pseudopodial apertures. The arenaceous shell is, properly 

 speaking, not a true shell secreted by the animal, since it is 

 simply composed of particles of sand united together by some 



