The Unicellular Organisms. 9 



pieces, it is only those fragments which have a nucleus (in the 

 case of the multinucleate forms such as Pelomyxa, already 

 referred to), or a fragment of the nucleus where there is but 

 one, that can reproduce the amoeba of which they are a 

 fragment. Bits of detached protoplasm, minus all trace of 

 the nucleus, lead for a time what has been described as a 

 "pseudo-existence," but ultimately decay; during this brief 

 existence, they may perform movements, but these have an 

 abnormal character without the dominating nucleus to direct 

 them. Again, the nucleus of many tissues in the higher 

 animals has been observed to preside over such functions as 

 the formation of yolk in ova, the budding of plant cells ; 

 and, in short, it is clear that the functions of the protoplasm 

 are largely directed by the nucleus. ^ 



Before leaving the amoeba, there is one important event in 

 its life that must be referred to. At times, when circumstances 

 are unfavourable — if, for example, the medium in which the 

 animal is living becomes too dry — the amoeba will surround 

 itself with a delicate skin excreted by th^ protoplasm. In this 

 encysted condition it can survive a degree of dryness which 

 would be fatal to it in its tiaked and unprotected condition. 



The Bell Animalcule {Vorticella). 



The organism known as the Bell Animalcule belongs to 

 the same great division as that which contains the amoeba, 

 but to a different group ; to this group the name " Infusoria " 

 has been given, originally from the fact that various members 

 of it were to be found in organic infusions. The Vorticella 

 is a social, but not a colonial, form common in fresh water ; 

 numbers are found Uving closely together. The creature, as 

 is shown in the accompatiying figure (Fig. 4), has somewhat 

 the appearance of a wine-glass supported on a long stalk. 

 When the animal is undisturbed, this stalk is elongated to its 

 full ; if the slide upon which a number of the organisms have 

 been placed for examination be jarred, they will contract, and 

 the long stalk is then seen to be thrown into a spiral. At the 

 same time a circle of rapidly moving filaments, which deck the 

 free end of the infusorian, are retracted also. 



