PKOTOZOA. 13 



The ciliated Infusoria are composed of a cuticle lined -with a 

 layer of gelatinous matter [endosarc] filled with chyme or a semi- 

 fluid substance, within which the particles of food rotate. Besides 

 the cilia, many Infusoria are furnished with bristles, hooks, &c., 

 and some with thread-cells [trichocysts]. 



In most Infusoria, as well as in Amoeba and others, certain clear 

 spaces or contractile vesicles exist. Other clear spaces [vacuoles] 

 sometimes make their appearance in every part of the body. 

 They vary in size, number, and position. 



A few species are found in the sea ; others are intestinal (Opa- 

 linidae, Belantidium, Plagiostoma, &c.). Opalinidae were supposed 

 to be the earlier stages of the Tremat,)de worms. 



Reproduction is by fusion or by gemmation, as well as bv the 

 nucleus at certain periods breaking up into fragments, each deve- 

 loping into the parental form. 



Without retractile tubes. 



Moving by cilia CILIATA. 



Moving by flexible filaments FLAGELLATA. 



With retractile tubes .. SUCTOIUA. 



Order I. CILTATA. 

 STOMATODA. 



Body more or less provided with vibratile cilia. No filaments 

 [flagella]. 



The cilia, which are organs of prehension as well as of motion, 

 are expansions of the cuticle [exoplasm]. In the majority of the 

 Infusoria, however, the cuticle is "nothing but a lifeless exuda- 

 tion of the surface;" where it exists it is seen under various 

 forms : in Dictyocysta it assumes the form of "lattice-like" shells ; 

 in Vaginicola it is a protective sheath. 



Some species, as in Vorticetta, are attached to foreign bodies 

 by a long and contractile pedicle. Torquatella is a marine Infu- 

 sorium without cilia; Eay Lankester regards it as a section of 

 Ciliata which he calls Calycata. 



The great majority of the Infusoria belong to this order, which 

 has been divided into four suborders or sections dependent on 

 the position of the cilia : in Holotricha they are dispersed, in 

 Heterotricha a longer series is found near the mouth, in Hypo- 

 tricha they are confined to the under surface of the body, and in 

 Peritricha they are arranged round the mouth. 



