40 MANUAL OP ZOOLOGY. 



The ' sareode ' whicli forms such a distinctive feature in 

 all the Protozoa, is a structureless albuminous substance, not 

 possessing 'permanent distinction or separation of parts,' 

 but nevertheless displaying- all 'the essential properties and 

 characters of vitality,' being capable of assimilation and ex- 

 cretion, of irritability, and of the power of contraction so as 

 to produce movements, strictly analogous, in many cases, to 

 the muscular movements of the higher animals. In some, 

 too, the sareode possesses the power of producing an external 

 case or envelope, usually of carbonate of lime or flint, and 

 often of a very complicated and mathematically regular struc- 

 ture. 



The most characteristic organs of locomotion amongst the 

 Protozoa are known as ' pseudopodia,' and consist simply of 

 prolongations of the sarcodic substance of the body, which 

 can usually be emitted from the greater portion of the general 

 surface of the body, and are capable of being again retracted 

 and of fusing completely with the body- substance. 



2. Classification of the Protozoa. The sub-kingdom Pro- 

 tozoa is divided into three classes, viz. the Gregarinidce, the 

 Rhizopoda, and the Infusoria. In the Infusoria only is a mouth 

 present, and hence these are sometimes spoken of as the 

 * Stomatode ' Protozoa, -whilst the two former classes collec- 

 tively constitute the ' Astomata? 



The following is a tabular view of the divisions of- the 

 Protozoa : 



Class I. GREGARINIDJE. 



Class II. RHIZOPODA. 

 Order 1. Amoebea. 

 ,, 2. Foraminifera. 

 3. Radiolaria. 

 ,, 4. Spongida. 

 Class III. INFUSORIA. 

 Order 1. Suctoria. 

 2. Ciliata. 

 3. Flagellata. 



3. CLASS I. GREGARINIDJE. The Gregarinidce may be de- 

 fined as parasitic Protozoa, which are destitute of _a mouth and 

 do not possess the power of emitting ' pseudopodia* They con- 

 stitute the lowest class of the Protozoa, and comprise certain 

 microscopic animals which are parasitic in the alimentary 

 canal of both invertebrate and vertebrate animals. They 

 have, however, a special liking for the intestines of certain in- 

 sects, being commonly found abundantly in the cockroach. 



Nothing anatomically could be more simple than the struc- 



