56 



CILIATE PROTOZOA 



\,u,„„ llu- most boautiful forms of pond life are the bell- 

 animalcuies, many of whicl>arc of the genus Vortudla (Hgs. 30,31)^ 

 Various species may be found as mmute, ^o ourless bod^s 

 fastened .0 weeds by stalks which contract at the shghtest 

 disturbance of the water. Some of them also appear m infusion 



The body of a Vorttcella is 

 outwardly shaped Hke a bell, 

 but has no hollow within, the 

 bell being filled with a mass 

 of protoplasm. In the place 

 of the handle is a long stalk, 

 by which the animal is 

 fastened to some sohd object. 

 Animals which are thus fixed 

 are said to be sessile. The 

 bell can be bent upon the 

 stalk. The wide end of the 

 bell has a thickened rim, 

 within which is a groove, the 

 peristome. On one side there 

 FiG. 30.— A group of individuals of Vorti- passes from the peristome, 



cella in various phases of the life- (JqWU into the maSS that fills 



a.. Ordm^'ldividual ; b., the same contracted ; c, tfic bcU, a tubC Which iS the 

 ordinary fission ; <i., a later stage of the same ; c, crnl1p>+ Thp fir«;f nart of thm 

 •rec-swimming individual produced by ordinary gUliei. 1 ilC iilbL pd.it Ul Liiis 



tis&ion ; /.. /'. two modes of fission to form a con- • ,,j\Af:,r fViorj +ViP rp^f ur\(\ 

 jugant ; g.. conjugation. 1^ WlUCi tllctll tiic icsL, a.ii\x 



the name vestibule is some- 

 times restricted to it. The part of the upper surface which 

 is encircled by the peristome is known as the disc. It is not 

 level, but slopes, being raised on the side where the gullet lies. 

 The disc can be retracted, and the rim of the peristome drawn 

 inward over it. Around the edge of the disc and down into the 

 vestibule two rows of cilia wind spirally counter-clockwise, the 

 inner long and upright, the outer short and slanting outwards. 

 In the vestibule the members of the outer row beat together to 

 form an apparent undulating membrane. There are no cilia 

 elsewhere upon the body. 



