92 



ZOOLOGY 



SECT. 



trichocysts (trch.). When the animal is irritated, more or fewer of 

 these suddenly discharge a long delicate thread. In a specimen 

 killed with iodine or osmic acid the threads can frequently 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 

 Paramo3cium being thus considerably in advance of those of Amoeba. 

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



Mg.nu 



FIG. 71. Paramoecium caudatum stages in conjugation. <jul. gullet ; mo. mi. mega- 

 nucleus ; mi. nu. micronucleus ; Mg. nu. reconstructed meganucleus ; Mi. nu. recon- 

 structed micronucleus. (From Parker's Biology, after Hertwig.) 



mouth, where the cortex and cuticle are less resistant 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 

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

 of both nuclei. As already mentioned, the meganucleus divides 

 directly, the micronucleus indirectly. Fission is never associated 

 with ency station as it is in Euglena. 



Under certain conditions multiplication by fission is interrupted 

 by conjugation. In this very remarkable and characteristic process 

 two Paramoecia become applied by their ventral surfaces (Fig. 71, A), 



