DOCTRINE or THE ACINETA-FOEMS. 97 



common form, others not unfrequently presented themselves 

 whose spherical body was enclosed in a usually wide case, 

 which was produced into a hollow funnel-shaped peduncle. 

 This case presented equidistant annular constrictions, alter- 

 nating with acute, parallel, angular ridges. Most of the 

 indi\iduals in this condition were unarmed ; but occasion- 

 ally Stein noticed them to be firrnished with numerous capi- 

 tate tentacles. 



On the other hand. Stein observed that, in the older cysts 

 of VorticeUa microstoma, the enclosed parent-vesicle had 

 undergone a change. Its naturally smooth, even siu-face, 

 almost everywhere closely fitted to the cavity of the cyst, 

 was in many places separated from the cyst-wall and de- 

 pressed towards the interior, in deep sinuosities, whilst in 

 other parts the parent-cyst was protruded into cseca — which 

 from their considerable size impinged with such force against 

 the wall of the cyst, that it appeared as if they were endea- 

 vouring to rupture it. 



These metamorphosed stages of the Vorticella-cysts, as 

 Stein fui'ther remarks, appeared to merge imperceptibly into 

 the above-described undeveloped conditions of the Podo- 

 2ihry(e ; it being assumed that the vesicular dilatations of 

 the parent-vesicle within the Vorticella-cysts were only the 

 commencement of a still greater enlargement of the parent- 

 vesicle ; whose forcible extension ultimately ruptnred the 

 walls of the containing cyst. In cases where the cyst is dis- 

 tended uniformly by the parent-vesicle contained within it — 

 which Avould happen when the cyst is free all round — the 

 Vorticella-cyst with its contents would of course be trans- 

 formed into an Act'mophrys ; but when this uniform disten- 

 sion in all directions is in any way prevented, in consequence 

 of the cyst being attached to some solid substance, all the 

 Vorticella-cysts would be transformed into Podopkryce, sup- 

 ported on longer or shorter peduncles.'^ 



These are the real facts upon which Stein supports the 

 doctrine of the transformation of Vorticella-cysts into Podo- 

 pkryce. For the circumstance that in infusions containing 

 cysts of VorticeUa microstoma, Podopkryce afterwards made 

 their appearance, can certainly not be regarded as decisive 

 in favour of the notion which would view the two Infusoria 

 as standing in any connection of development. 



With respect to the second proposition concerning the 

 transformation of the motile embryo into a VorticeUa, Stein 

 admits that he has not directly observed it, as in spite of 



* Stein, ' Infusiousthiere.,' p. 145. 



