30 COMPARATIVE ANATOMY AND PHYSIO LOGY, 



I. Ciiiata, as Paramoecium, Vorticella, and 

 others ; the cilia are either regularly distributed over 

 the cell, and are, for the most part, subequal in size 

 (Paramoecium) (Fig. 3 I.) ; or some are much larger 

 than the rest (Stentor) ; or the cilia are ordinarily con- 

 fined to a spiral circlet around the mouth (Vorticella), 

 and are only occasionally found on other parts of the 



Fig. 3 ii. A, Noctiluca miliaris ; B, with buds ; c, section. 

 n, Nucleus ; /, flagellum ; t, tentacle ; d, denticle ; an, anus. 



body ; or, finally, they may be limited to the so-called 

 ventral surface (Euplotes) ; in the Peritricha, as the 

 group to which Vorticella and its allies belong is called, 

 there is often an elongated aboral stalk, which some- 

 times exhibits a remarkable power of rapid contraction. 

 II. Flagellaia ; a number of forms are grouped 

 by some writers under this head ; of such as are 

 almost indubitably animal, Noctiluca (Fig. 3 IL), the 

 animalcule which causes much of the diffused phos- 

 phorescence of the sea, is one of the best known. 



I 



