156 



PROTOZOA 



truncate cone set obliquely so that its wide base hardly projects 

 at one side, but is tilted high on the other ; the edge of the bell 

 is turned out into a rim or " collar," separated from the disc by 

 a deep gutter. The collar, habitually everted or even turned 

 down, contracts over the retracted disc when the animal is 

 retracted (E^), which is brought about by any sort of shock, or 

 when it swims freely backwards. For the latter purpose a 

 posterior ring of cilia (or rather membranellae) is developed 

 round the hinder end of the bell (A, cr, W). The cilia of the 

 adoral wreath are very strong, united at the base into a con- 



FiG. 59. — Stentor poly- 

 morphus. I, Young 

 iiidiviflual at- 

 triclied. extended ; 

 II, adult in fission, 

 contracted ; cv in 

 I, afterent canal of 

 contractile vacu- 

 ole ; in II, con- 

 ti'actile vacuole ; N, 

 nioniliform niega- 

 nucleus (micro- 

 nuclei omitted) ; 

 0, mouth ; the fine 

 lines are the myo- 

 neme fibrils. (From 

 Verworn.) 



tinuous membrane, and indeed themselves partake of the com- 

 posite nature of membranellae. The wreath forms more than 

 one turn of a right-handed spiral, the innermost turn ending 

 abruptly on the disc, the outer leading down into tlie mouth at 

 the point where the disc is most tilted and the groove deepest.^ 

 The pharynx (2?) is long, and contains an undulating membrane 

 {u.m) on its inner side projecting out through the mouth, and 

 numerous cilia ; it leads deep into the body (2?). The first part 

 is distinguished as the " vestibule " {v), as into it opens the anus, 

 and the contractile vacuole {cv.), the latter sometimes opening by 

 u reservoir (r). The body contains in the ectoplasm myonema- 



' Outside the principal wreath is another of fine cilia ("paroral"), standing 

 out at an an^le. 



