48 THE SUB-KINGDOM PROTOZOA. 



presence of any such periodically contracting vesicles in the aforesaid and 

 other allied types, though in many of these, irregularly formed and per- 

 manently conspicuous vacuoles or inter-parenchymal spaces, having no 

 fixed location nor rhythmically contractile motions, were found to occur. 

 These observations having been confirmed by repeated and most careful 

 examination of the two generic types just named, the presence or absence 

 of a contractile vesicle is now definitely accepted by the author as affording 

 a ready means of distinguishing between unicellular animal and vegetable 

 organisms. In those instances in which the possession of a contractile 

 vesicle has been attributed to Volvox globator, as by Busk * and other inves- 

 tigators, it would appear probable that either Uroglena, Syncrypta, or some 

 other of the several Volvox-like animal organisms formed the subject of 

 observation. 



* ' Transactions of the Microscopical Society,' p. 35, 1852. 



