xcvi THE BEGINNINGS OF LIFE. 



more rows of cilia, by means of which, before effecting its 

 exit, it moves about in the cavity in which it is contained. 

 Its body is made up of a finely-granulated sarcode, contain- 

 ing a band-like nucleus in its posterior portion, and closely 

 adjacent to this there is a distinct contracting vesicle. No 

 mouth is visible, but on the whole it presents a form which 

 would seem easily convertible into a Vorticella; and this 

 Stein believes to be its next developmental stage. 



A more or less similar life-history is, he believes, the rule 

 with very many of the Ciliated Infusoria. Cienkowski, 

 Kolliker and others, however, believe that Stein has con- 

 founded certain Acinetce with members of the family Actino- 

 phryna, and although they fully admit that Acinetce. do de- 

 velop ciliated embryos in their interior similar to those 

 described by Stein, Cienkowski and some others believe 

 that such ciliated embryos are reconverted into Aa'neta-\ike 

 organisms, and that they do not give rise to VorticelliB as 

 alleged by Stein. Cienkowski's observations * on one occa- 

 sion were undoubtedly sufficiently positive to entitle him to 

 come to the conclusion that ' from the Acme/a-embryo, after 

 a prolonged motile stage, another Acineta is formed/ but, as 

 he himself admits, his ' observations do not, of course, show 

 that it is impossible that the motile Acine/a-embryo should 

 be transformed into a Vorticella, and a Vorticetta-cyst into 

 an Acineta' 



Cienkowski's observations would only really militate 

 against those of Stein, if we were to assume, what is highly 

 improbable, viz., that the developmental metamorphoses 

 amongst this group of animals are in all cases the same. 

 Much evidence exists, pointing to the conclusion that 

 there is the greatest variability on different occasions, and, 

 consequently under the influence of different sets of con- 



1 'Journ. of Microsc. Science,' 1857, p. 96. 



