l'J2 PROTOZOA 



tide on iho outside of the luulv, ^'liich in the 'ametahola' is firm; in the 

 others very llexible. The cutiele is covered witli cilij — small vil)rating 

 processes which move tOL^elher, and serve not only as organs of loco- 

 motion, but liy creating \ortices in the water bring food to the organism. 

 They furnish the most important characteri-tic of the class (i'lg. 150). 



The presence of a cuticle necessitates a cytostome, except in the para- 

 sitic species, since fooil particles cannot be taken in at every point. At 

 the cytostome the cuticle with its cilia forms a funnel-like food tulje (cyto- 

 pliarynx) into the protoplasm. At tl^e botlom tlie cuticle is interrupted 

 so that water and protoplasm are in contact. By the action of tlie cilia 

 food particles arc taken into the cytophar}'nx and pressed against the 

 protoplasm, forming a small enlargement which finally sinks into the 

 substance as a food vacuole {na) wliich, by the streaming of the protoplasm, 

 is carried aljout in the body. The digestiljle portions are aljsorlied, 

 and those not capable of digestion are cast out of the body at a fixed 

 point (cylopygc) usually not recognizable at other times (fig. 150.3). 

 Contractile vacuoles (rv) are lacking only in parasites and marine species. 

 They are constant in numlser and position, and frequently have attercnt 

 ducts which empty into the vacuole, the vacuole in turn forcing the fluid 

 to the exterior. 



Trichocysts, nettle bodies, and muscular fibrilL'B occur in some species. 

 Trichocysts are minute rods yertical to the surface in the cortical layer, which 

 under the inlluence of reagents (chromic acid) elongate into threads penetrating 

 the cuticula. To these have been ascribed defensive functions; others regard 

 them as tactile structures. They have no connection with the cilia. Nettle 

 bodies are extremely rare. Muscle fibres lie between ectosarc and cuticle, and 

 cause cjuick convulsiye motions of the animal. 



There are two nuclei physiologically unlike. The larger of these 

 (nucleus of older writers, inacroniiclciis) is a large oval, rod-like, or spiral 

 Ijody, deeply staining with microscopic stains, and surrouirdcd with a 

 membrane. It controls all the common vital functions of tire animal 

 (motion, feeding, etc.). Beside it or in a depression in it is the much 

 smaller mirro)iiirlciis (nucleolus or paranucleus of older authors) ■\\hich 

 stains less deeply. In all sexual processes it comes to the front and can 

 be called the sexual irucleus. 



Multiplication of Ciliala occurs by liinarv fission (fig. 150); more 

 rarely, and then only in the encysted condition, by division into numerous 

 parts. Budding is known in the Teritricha atid Suctoria. In fission first 

 the micronuclcus (li\-ides milotically, and then the macronucleus separates 

 by elongation and constriction. The old cytostome persists in the an- 

 terior offs])ring, jiul often an outgro\\'lh from it (2, o') passes into the 

 posterior half and de\elops into a new mouth. 



