32 



INVERTEBKATE AXIMALS. 



shell amongst the Foraminifcni , and it is often called the " nauti- 

 loid " shell, from the close resemblance which it bears in shape to the 

 well-known shell of the Pearly Nautilus. It was, in fact, this ex- 

 ternal similarit}'" which induced the older naturalists to place the 

 Foraminifira amongst the ilnUusca in the neighbourhood of the 

 Cuttle-fishes. There are numerous other types of shell, all of which 

 can be referred to the manner in which the primordial segment 

 becomes constricted or segmented ; but the two forms above men- 

 tioned may be taken as sufhcient examj^Ies. It may be mentioned, 

 however, that there are forms in which the new segments are added 

 in a very irregular manner, and the resulting shell has no very defi- 

 nite shape. 



The great majority of the Foraminifera are inhabitants of the 

 sea, and they are mostly very minute. A few living forms may 



Fig. 10. — Organisms in tlie Atlantic 

 Ooze, chiefly Foraminifera (Glohiger- 

 ina and Textvlaria), with Fohjcystinn 

 and sponge-spicuk-s ; highly magni- 

 fied. 









■-•^ 





Fig. 11.— Section of Gravesend Chalk, ox- 

 amined by transmitted liglit and higlUy 

 magnified. Besides the entire shells of 

 Globigerina, Rntalia, and TextuJaria, 

 numerons detached chambers of Globi- 

 gerina are seen. 



reach a quarter of an inch, half an inch, or even more than an inch 

 in diameter. The commoner forms may usually be found by ex- 

 amining with a lens the sand of the sea-shore in places where there 

 is a large intermixture of broken shells and fragments of other 

 marine animals. Many forms live in the open ocean floating near 

 the surface of the water. Others li\'e on the bottom of the sea up 

 to the greatest depths which haVS yet been examined by the dredge. 

 At great depths in the sea — dcjjths, it may be, of over two or three 

 thousand fathoms — the bottom is often found to be covered with 

 a whitish chalky mud, which is seen under the microscope to be 

 almost entirely made up of the shells of various Fi»-iniiinifera, and 



