90 



ZOOLOGY 



SECT. 



these suddenly discharge a long delicate thread, which, in the 

 condition of rest, is very probably coiled up within the sac. In a 

 specimen killed with iodine or osmic acid the threads can fre- 

 quently be seen projecting in all directions from the surface (C). 



Food, in the form of small living organisms, is taken in by 

 means of the current caused by the cilia of the buccal groove. The 

 food-particles, enclosed in a globule of water or " food-vacuole " 

 (/. vac.), circulate through the protoplasm, when the soluble parts 

 are gradually digested and assimilated. Starchy and fatty matters, 

 as well as proteids, are available as food, the digestive powers of 

 Paramcecium being thus considerably in advance of those of Amoeba. 

 Effete matters are egested at a definite anal spot posterior to the 

 mouth, where the cortex and cuticle are less resistent than else- 

 where. The whole feeding process can readily be observed in this 

 and other Infusoria by placing in the water some insoluble colour- 

 ing matter, such as carmine or indigo, in a fine state of division. 



Reproduction. Multiplication takes place by transverse 

 fission (D), the division of the body being preceded by that of both 

 nuclei. As already mentioned, the meganucleus divides directly, 

 the micronucleus indirectly. 



It has been proved, however, that multiplication by binary 

 fission cannot go on indefinitely ; but that after it has been repeated 



Mg.nu 



FIG. 70. Paramoecium caudatum, stages in conjugation, gul. gullet ; mg. nu. meganucleus ; 

 mi. nu. micronucleus ; Mg. nu. reconstructed meganucleus ; Mi. nu. reconstructed micro- 

 nucleus. (From Parker's Biology, after Hertwig.) 



a certain number of times it is interrupted by conjugation. In 

 this very remarkable and characteristic process two Paramcecia 



