6 PEOTOZOA. 



and Foraminifera ; Polycystina (=Radiolaria); Gregarinoidea ; 

 Infusoria ; and Spongia. In Infusoria he places Vibrio, Bacterium, 

 and Volvox ; his order Cymozoida includes the first two, while 

 Volvox, together with Monas, Astasia, Noctiluca, &c., are com- 

 prised under Mastigophora. Huxley divides the Protozoa into 

 Monera (including Foraminifera) and Endoplastica (including 

 Protoplasta (Amoeba, &c.), Gregarinida, Infusoria, &c.). 

 For the present three classes may be recognized : 



Without a mouth. 



Without pseudopodia GREGARINIDA. 



With pseudopodia EHIZOPODA. 



With a mouth ... .. INFUSORIA. 



Class I. RHIZOPODA. 



SARCODINA. 



Minute aquatic animals, moving by an extension of their sub- 

 stance (pseudopodia) ; with or without a shell, and without a 

 mouth. 



The pseudopodia or extending portions of the substance are 

 sometimes confined to one side of the body ; they may be merely 

 short lobular dilations, or, as is generally the case, long fila- 

 mentous processes capable of multiplying themselves and coales- 

 cing whenever they come in contact. 



The nucleus is a hyaline vesicle generally containing a bluish 

 nucleolus ; the central capsule is a membranous sac separating the 

 nucleus from the outer protoplasm [sarcode]. The latter contains 

 granules and certain yellow cells [sarcoblasts] supposed to be 

 parasitic organisms (Cienkowski), an incipient form of liver 

 (Hackel), and reproductive organs (Wallich). Eecent observa- 

 tions seem to show that the " reproductive cells " are contained 

 in the central capsule ; and the yellow cells are found by Hackel 

 to contain a substance which cannot well be distinguished from the 

 starch of plants. According to Sir W. Thomson, the capsule is 

 " absent, or, at all events, exists in a very modified form in the 

 more typical groups." 



Contractile vacuoles are certain cavities having a rhythmical 

 movement : their function is possibly respiration. 



Four orders are indicated, but exceptions occur to most of their 

 characters : 



