158 



BIOLOGY. 



[BOOK ii. 



In the amrebse we behold the very birth of the digestive 

 function. Alimentary particles glue themselves on the viscous 

 surface of the amoeba at any point whatever of this surface ; then 

 penetrate by degrees into the central parts of this elementary 

 organism, by digging for themselves, in some sort, a temporary- 

 digestive canal, which closes behind them. Finally, the aliment 

 dissolves ; its molecules incorporate themselves gradually with 

 the substance of the amo3ba and the residuum not assimilable 

 is expulsed through some point of the surface. The same 

 alimentary process is observable in the rhizopods with this 

 difference, that the viscous prolongations or pseudopods of the 

 animal roll themselves, first of all, round the alimentary par- 

 ticle. Things take place exactly in the same way in the actino- 

 sphcerium which, however, is an organism differentiated into 

 cells. (Fig. 4). 



In the acinetous infusoria the radiating appendices clasp the 



prey, which is usually another 

 infusorium whose soft substance 

 lets itself be liquefied and passes 

 along the appendices as along 

 tubes, to come finally to accu- 

 mulate in droplets in the par- 

 enchyma of the animal. 



The specialisation which com- 

 mences already to be discernible 

 in -the acinetous infusoria takes 

 increased point and pith in other 

 animals of the same class. There 

 is not yet any digestive appar- 

 atus : but there is a special 

 orifice of ingress and sometimes 

 also a special orifice of egress. The aliments penetrate by the 

 orifice consecrated to that use, and which is furnished with 

 vibratile cilia, making for themselves a way through the paren- 

 chyma as in the previous case ; then the residuum is expulsed. 



FIG. 4. 



Actinospfuzrivm. a, alimentary fragment 

 penetrating into the cortical layer ; 

 6, c, central parenchyma; d, globules 

 of nourishment ; e, pseudopods of the 

 cortical layer. 



