MACKIE — FIEST. TEACES OF THE SUCCESSION OF LIFE. 353 



Secondary and Tertiary formations, the animals, altliongli they put 

 on nantiloid or Nautilns-resembling forms, are not truly such 

 chambered shells as those of the cephalopod, but are in reality a 

 congeries of either constricted, flattened, or inflated globular minute 

 masses of shell-covered jelly-like flesh, or sarcode, which are so con- 

 gTegated together by the natural imperfect self-division or fissi- 

 partition of one from the other. The original animal consists of a 

 mere Httle globular mass, apparently without nerves or organs of nu- 

 trition or digestion, the enveloping cuticle of which hardens into a 

 calcareous, homy, or siliceous shell, full of minute pores, through 

 which the sarcode is protruded in fine threads for the purposes of 

 prehension or locomotion. 



At the period of gTOwth or self-division this sarcode is exuded 

 and forms a second globule, the containing cuticle of which hardens 

 in the like manner into an enveloping shell, but which remains 

 attached on the side whence it was exuded to the parent globule. 

 These repeated exudations take place on more or less regular plans ; 

 sometimes each overlaps the other to form a nautilus-like forami- 

 nifer ; sometimes they are developed in a straight line or a continuous 

 slight curve ; sometimes the arrangement is spiral ; sometimes on a 

 flat plane ; and sometimes commencing in their young state on one 

 plan, they are continued on to their adult state on another. 



From the Foraminifera we ascend to the sponges, still gelatinous 

 animals, but having an internal support of horny, calcareous, or sili- 

 ceous threads or spines (spicula) , and also inhalent and exhalent chan- 

 nels for the in-draught and expulsion of currents of water, by which 

 means the sustenance of the sponge is obtained. 



The next class in the scale of animal-life shows a structural plan of 

 a radiate or star-like character. There is a central plate, point, or 

 cavity whence the parts of the organism radiate, like the spokes of a 

 wheel from its nave. This is seen in the polypi or coral-animals, the 

 sea-anemones (Actinia), and the hydras of our ponds. We see the 

 like type-form in the jelly-fish and little balloon-like Beroes (Gy- 

 dijjpe pileus) ; and we see it also in the sea-urciiins and star-fish, 

 and in the fossil crinoids or lily-animals. 



In the Articulata, the typical form of structure is that of jointed 

 segments or rings, as we observe in the common earth-worm and 



