i 5 6 



PROTOZOA 



CHAP. 



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 2 ), 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, E 3 ). The cilia of the 

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



Fig. 59. Stentor poly- 

 morphus. I, Young 

 individual at- 

 tached, extended ; 

 IT, adult in fission, 

 contracted ; cv in 

 I, afferent canal of 

 contractile vacu- 

 ole ; in II, con- 

 tractile vacuole ; N, 

 moniliform mega- 

 nucleus (micro- 

 nuclei omitted) ; 

 o, 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 the mouth at 

 the point where the disc is most tilted and the groove deepest. 1 

 The pharynx (p) 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 (p). The first part 

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

 and the contractile vacuole (c.v.), the latter sometimes opening by 

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



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

 out at an angle. 



