38 



INVERTEBRATE ANIMALS. 



of cilia. There is a third smaller group — the Suctoria — in which 

 the body is furnished with contractile tentacle-like filaments, which 

 end in little discs, and are used as sucking-tubes. It will not be 

 necessary to do more than mention the Suctorial Infusoria here ; 

 but the two groups of the Ciliata and Flagellata require more 

 detailed attention. 



Fig. 17. — Ciliated and Flagellate Infusoria. A, Bursaria truncatella, enlarged 50 

 times. B, Nyctoth&ms cordiformis, enlarged 150 times. C, Amphileptus anser, 

 enlarged 120 tunes. D, Ceratium tripos, enlarged 250 times, with its carapace and 

 single flagellum. E, Monosiga angn^Uitit, enlarged 2500 times; n Nucleus; c 

 Contractile vesicle ; / Flagellum ; m Membranous collar surrounding tlie base of 

 the flagellum. (After, or copied from, Saville Kent.) 



The Ciliated Infusarid may be defined as Protozoa which are pro- 

 vided with a mouth, and usual/// a short gullet and a distinct amis. 

 Their bodies cousist of soft semi-fluid prutuplasm (" endoplasiii '■) en- 

 closed by a more or less complex external la/jer {^'' exoplasm") ; and 

 the external siirface is parti// or wholl// covered with vibrating cilia. 

 They are mostly simple free-swimming organisms ; but they some- 

 times form colonies by budding, and are fixed to some solid object 

 in their adult condition. As types of these two sections of the /«- 

 fusoria, we may take respective'y Paramecium and Vorticella. 



