ANIMALCULES 493 



are conducted into the mouth. Within the body two pulsating 

 vacuoles can be seen, one at each end, and there are also two 

 bodies of nuclear nature, which are placed close together. One of 

 them is large (macronucleus), and the other small (micronucleus). 

 They pass through a series of very complicated changes before 

 the animal undergoes transverse splitting or fission, which is here 

 the characteristic method of multiplication. 



A very large section of the Infusoria are characterized by the 

 presence of cilia, the arrangement of which differs in different 

 species, and these constitute the group of Ciliata. We may 

 take as a second example of this division the Bell Animalcule 

 (^Vorticelld) (fig. 301), which is commonly found attached to water- 

 weeds, or it may be to aquatic animals, such as the little red worm 

 Tubifex (p. 431). Here the body is of bluntly conical form, with 

 the narrow end drawn out into a long stalk, firmly fixed to the 

 object upon which the animal lives. When fully expanded, 

 it can be seen that the cilia are limited to the broad end of the 

 body, on which they are arranged in a short spiral, while smaller 

 cilia are continued down into a depression, which may be compared 

 to that seen in the Slipper Animalcule, for it leads into a short 

 gullet of the same kind. Within this depression there is a soft 

 spot through which the undigested remains of the food are ejected. 

 The wreath of cilia produces currents, which set into and out 

 of the mouth -depression, carrying food and dissolved oxygen 

 inwards and waste matters outwards. As in a Slipper Animalcule, 

 the protoplasm is divided into a softer central endosarc and a firm 

 external ectosarc, the latter being continued into a fibre which runs 

 in a wavy manner through the stalk. If Vorticella is alarmed in 

 any way, the free end of the body is folded in, and, at the same 

 time, the elastic stalk is thrown into the form of a spiral by the 

 shortening or contraction of the fibre it encloses. 



Within the body one pulsating vacuole can be seen, and also 

 two nuclei, the big one having a very characteristic horse-shoe 

 form. Multiplication is effected by longitudinal splitting, one of 

 the two new individuals remaining on the stalk, while the other 

 becomes detached, being rowed about by the cilia till a suitable 

 spot is reached, when it becomes attached, and develops a new 

 stalk. 



Some of the near relatives of the Bell Animalcule form colonies 

 by means of fission, the new individuals remaining attached instead 



