46 MANUAL OF ZOOLOGY sect, i 



vacuoles (V. vac) are present. Each is connected with a 

 series of radiating spindle-shaped cavities in the protoplasm 

 which serve as feeders to it ; after the contraction of the 

 vacuole these cavities are seen gradually to fill, apparently 

 receiving water from the surrounding protoplasm ; they then 

 contract, discharging the water into the vacuole, the latter 

 rapidly enlarging while they disappear from view ; finally 

 the vacuole contracts and discharges its contents externally. 



The cortex contains minute radially-arranged sacs called 

 trichocysts {trek). When the animal is irritated, more or 

 fewer of these suddenly discharge a long delicate thread 

 (C), which, in the condition of rest, is very probably coiled 

 up within the sac. 



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 proto- 

 plasm, where the soluble parts are gradually digested and 

 assimilated. Effete matters are egested at a definite anal 

 spot posterior to the mouth, where the cortex and cuticle 

 are less resistant than elsewhere. The whole feeding pro- 

 cess can readily be observed in this and other Infusoria by 

 placing in the water some insoluble colouring matter, such 

 as carmine or indigo, in a fine state of division, the minute 

 particles of the colouring matter, which are taken into the 

 mouth in the way described, being readily observed as they 

 become received into food-vacuoles and circulate in the 

 central protoplasm. 



Multiplication takes place by transverse fission (D), the 

 division of the body being preceded by that of both nuclei. 

 It has been proved, however, that multiplication by binary 

 fission cannot go on indefinitely, but that after it has been 

 repeated a certain number of times, it is interrupted by 



