INFUSORIA. 



41 



improbable tliat the contractile vesicles should be looked upon as 

 corresponding with the water- vessels of the lower groups of Worms, 

 and as having the function of excretory, rather than of circulatory 

 organs. 



Reproduction in Pararmecium, may be effected simply by trans- 

 verse cleavage or fission of the body into two portions (fig. 19, B). 

 In other cases " conjugation " of two Paramoscia takes place. In 

 this process two individuals come together, and adhere closely to one 

 another by their ventral surfaces, in such a way that they present 

 the appearance of a single individual undergoing longitudinal fission 

 (fig. 19, C). Partial fusion of the conjugating individuals takes place, 

 and the nucleus and nucleolus pass through certain curious changes. 

 Ultimately, the conjugating individuals separate again, and each 

 probably then imdergoes repeated fission, and thus gives lise to fresh 

 Paramcecia. 



As a common and beautiful example of the Stalked Infusoria, we 

 may take the so-called Bell-animalcule ( Vorticella, fig. 20, C), which 



Fig. 20.— A, Stentor MiiMeri. B, VaginicoTa cnjstallina. C, Group of Vortuxllce. 

 D, Detached bud of VorticelUi, showing the posterior circlet of cilia. 



may be found in any stagnant pool attached to the stems of aquatic 

 plants. The body in Vorticella forms a kind of cup or " calyx " sup- 

 ported upon a long stalk, which is in turn fixed to some solid object. 

 The stem contains a contractile fibre in its interior, and the animal 

 can by this means push itself out or coil itself up with the utmost 

 rapidity. The vibrating filaments or ciUa are not scattered over the 

 whole surface of the bell-shaped body, but are collected to form a 



