Pbrticellina ■} tVFUSOBiAL animalcules. 53? 



modified by contraction (figs. 19, 20, 21.) The largest are not abova 

 l-24tli of a line in length; the smallest 1- 100th, The enclosing- 

 tunic is elastic and colourless, and stronger behind than in. front. 

 The divergent fibres are disposed in two bundles, one at each antelrioi* 

 angle; (fig. 16), they enjoy a considerable degree of motion; and 

 often, by theii* intertw ining or crossing, entangle small Infusoria or 

 other bodies. 



In many large Acineta forms, the divergent fibres are wanting 

 (fig. 17); such probably are in an earlier stage of metamorphosis ; 

 and subsequent to the completion of the encysting process of the 

 original Epistylis, 



The Acineta-bodies have no mouth ; it is indeed difficult, from the 

 toughness of their tunic, to efiect a rupture ; no food or stomach sacs, 

 likewise, can be foimd in them, their substance being homogeneous, 

 granular, soft, and containing, besides its very fine granules, some 

 larger globules, probably of oil (fat), a contractile sac anteriorly, 

 and an elliptic discoid granular nucleus, often accompanied by anothei" 

 smaller, finely granular, discoid globule, well defined. Both nuclei 

 are seen in fi.g. 18. 



The larger nucleus is the one destined to undergo the first change ; 

 this it does by the development of fine cilia aroimd its periphery, 

 which actively vibrate, and so cause its rotation. Whilst this goes on, 

 it increases in size, advances towards the anterior of the Acineta, 

 which takes on active contractions, and thereby ultimately ruptures 

 its integument, allowing the embryo (ciliated nucleus) to escape. 

 On its emergence, the embryo swims away rapidly by means of its 

 cilia : what further changes it undergoes it is yet to be discovered. 



However, the part the Acineta-body has to perform, is not com- 

 pleted by the production of the one embryo ; but the same process is 

 to be repeated again and again, until its formative granuhir mass is 

 used up, when the Acineta becomes a contracted, shrivelled, empty 

 sac (as seen in fig. 21), seated upon the persistent stalk. 



After the emission of an embryo, the Acineta-body contracts strongly; 

 some of its diverging fibres shorten, whilst others are entii'cly with- 

 drawn. This contracted condition, after lasting for a time, relaxes ; 

 the Acineta resumes its usual movements, the fibres spread out anew, 

 moving about as usual, in various directions ; and it finally regains 



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