40 



ZOOLOGY. 



Class IV. — I^-F^soRIA, 



FlageUate or ciliate (sometimes only ciUate in the early slage<) Protoso,!. 

 ihe body not changing inform, having a defirdle skin, and often ichMy or 

 jtartty xi/romded icith eUia; usually free, sometimes stalked or attached; ici'th 

 a mouth-'?pe liing and oisophagus, and rudiments of digesUte, circula- 

 tory (two or more contraciite vesicles), and reproducUtx organs (nucleus and 

 nucleolus), but with no distinclitely sexual organs. 



Order 1. FlageRata. — Bounded, oval, or pear-shaped organisms, usually 

 exceedingly minute, prorided with one or two flagella, with 

 an oral region, into which particles of food are thrown by 

 the flagellum ; with a nucleus and contractile vesicles, rarely 

 stalked, and with a calyx; sometimes aggregated: with a row 

 of cilia in the highest forms servinir as a locomotive appara- 

 tus ; reproducing h\ self-division oi by segmentation of the 

 protoplasmic contents of the body, the young being minute 

 oval bodies, provided with a flagellvmi (ilonas, Heteromita, 

 Koctiluca, Peridinium). 



Oraer 2. TentacuUfera (Suctoria). — Naked, not ciliated, protozoan', 

 with long, stiff, retractile arms or tentacles, provided with a 

 sucker at the i rd, t'\e arms hollow, conveying the food to 

 the digestive tavil^ ; originating from ciliated \-oung ; also 

 by self-di\nsion throwing off ciliated forms, and undergoing 

 conjugation (Acineta). 



Order 3. Ciliota (True Infusoria). — Body free and covered with cilia 

 (Paramecium, Stentor, etc.), or stalked, with the cilia con- 

 fined to the head end (Vaginicola and YortktUa, etc.); a 

 well-defined month and oesophagus ; a digestive cavity and 

 vent ; a largo nucleus, and two or more contractile vesicles. 

 Reproducing by self-division, budding or conjugating, and 

 producing monad-like young by self-division of the nu- 

 cleus ; sexuality doubtfully indicated. 



The followinsr diagram represents tlie relative position 

 •of the orders and classes of Protozoa, and in a ritde wav 

 their possible genetic relations : 



verlebrated .\nimals, p. 6i3'3\ " it is «till possible that the conjugation 

 of the Infusoria may be a true sexual process, and that a portion of the 

 divided endoplastules [striated nucleoli] of each may play the part of 

 the spermatic corpuscle, the conjugation of which with the nucleus of 

 the ovum appears, from recent researches, to constitute the essenci* 

 of the act of impiegnatioo." 



