62 INVERTEBKATE ANIMALS. 



shell amongst the Foraminifera, luvl it is often called the "nauti- 

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

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

 ternal similarity wliich induced tlie older naturalists to place the 

 Foraminifera amongst the Mollnsm iu the neighbourhood of the 

 Cuttle-fishes. There are numenius otlier tyjies of shell, all of which 

 can be referred to the manner in whicli the pi'imordial segment 

 becomes cousti'icted or segmeutefl ; but the two forms al)ove men- 

 tioned may be taken as sufficient examples. It may lie mentioned, 

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

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

 nite shape. 



The great majority of the Foramitufi-ra are inhabitants of the 

 sea, and they arc mostly ^"ery minute. A few living forms may 



Fig. 10.— Orgcinisins in llie Atlanlic 

 Ooze, cliii-fly Fnraitii iiifrra (Clotthin- 

 inn and Tr.,U:Uiriu), with r„l,i,!islina 

 ami spijiigc-siiiciih'M ; lii;,dily nia^^ni- 

 fi'il. 





^ig. 11.— Section of Gravesend Clialli, ox- 

 aniincd liy transniittoii iiglit and lii^ldy 

 iififjnilied. Besides llie entii'e slieil.s of 

 /!lohi:jrii na, U"l"lia., and Tej-Uilaria, 

 nnnie;ons detaelied cliambers of Glohi- 

 ncriini are seen. 



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

 in diameter. The cormnnner forms may usualiy l)e found by ex- 

 amining with a lens the sand of the s •a-slnire in places whei-e there 

 is a large intermixture of l;i-(iken shells and fi-agments of other 

 marine .•inimal.s. ilanj' forms live iu the open ocean flo.ating near 

 the surface of the watei'. nilurs live on the bnttom of the sea U]1 

 to the greatest depths wliich have yet been examined by the dredge. 

 At great dejiths iu the sea — depths, it may be, of over twii or three 

 thousand fathoms — tlie bottum is often fomid to lie covered with 

 a whiti.sh chalky mud, which is seen under the micidscope to be 

 almost entirely made up of the shells of vaiious Formuiiiifera, and 



