64 IXFUSOPJA. 



{fig* 12, k). In their dilated condition these ve- 

 sicles would seem to be filled with a clear fluid, 

 which suddenly disappears when they contract. 

 It may, in some cases, be noticed that the vesicles 

 are furnished mth branches or processes, and 

 Lachmann asserts that he has seen two such pro- 

 cesses issue from the large contractile space of 

 Steator polymorphiis, the one annular, running 

 beneath the surface of the ciliary disk, the other 

 longitudinal, proceeding to the posterior extremity 

 of the body. "WTien the vesicle contracts, both of 

 these " vessels " suddenly expand, the longitudinal 

 vessel, in particular, being seen to present nu- 

 merous dilatations. At the same time two rounded 

 expansions make their appearance in the annular 

 vessel, the one being situated in the neighbour- 

 hood of the anus, the other lying close to the 

 oesophagus, on the ventral surface of the body. 

 When the contractile vesicle reappears, both of 

 these vessels gradually decrease, " apparently ^Yith.- 

 out any contraction of their own." In healthy spe- 

 cimens of Bursaria, Ophryoglena, and Pavame- 

 chwif the contractile vesicles, together with their 

 associated vessels, assume a peculiar stellate form. 

 These and other similar appearances, observed in 

 the bodies of various InfusoAa, are supposed by 

 some to present us mth what may, perhaps, be 

 termed a rudimentary apparatus of circulation. 



It seems proper to distinguish the above con- 

 tractile vesicles from certain other clear spaces 

 which have received from Dujardin the name of 

 " vacuoles." These may make their appearance 

 in any part of the interior of the body, and are 

 usually observable within a short period after food 

 has been swallowed. They may readily be known 



