824 THE ANIMAL KINGDOM. 



the definiteness of outline conferred by the skeletal structures of many Gymno- 

 myxans. 



In the following pages the Protozoa are thrown into three divisions, depending 

 on their modes of locomotion and of obtaining solid food, as well as on the dominant 

 or adult phase of the life-history. For the Gymnomyxa the old term Rhizopoda is 

 retained. The Sporozoa, which must be regarded as Rhizopods adapted to an 

 endoparasitic life, are kept apart as Endoparasita. For the Acinetaria, Infu- 

 soria and Mastigophora, the designation Plegepoda is proposed, referring to their 

 mode of progression by means of a rapidly repeated stroke (n\rjyf)) of vibratile 

 processes. 



For Erythropsis agilis, a Protozoon (?) of very peculiar structure, with an eye 

 composed of a lens and pigment, known only from a single specimen, see R. Hert- 

 wig, M. J. x. 1885 ; C. Vogt, R. Hertwig, Z. A. viii. 1885. Metschnikoff (Z. A. 

 viii) states that he once found a very similar organism which he believes to have 

 been an Acinetarian. 



For Dumontia Opheliarum, an endoparasite in the coelome of the Chaetopod 

 Ophelia, which has a peculiar internal axis, a bilobed body with stable pseudopodia, 

 and vacuolate exoplasm, and a peculiar mode of gemmation, see Kunstler, Bull. 

 Soc. Zool. France, x. 1885. Kunstler is of an opinion that it is the type of a 

 new group of Rhizopoda. 



'Protozoa,' Butschli, Bronn's Klass. und Ordn. des Thierreicns, Leipzig, 

 1880-5 ; does not yet include the Acinetaria and Infusoria. 'Protozoa,' Ray Lan- 

 kester, Encyclopaedia Britannica (ed. ix), xix. 1885. 



PLEGEPODA. 



PROTOZOA in which the organism is provided with cilia, flagella, 

 or vibratile membranes as organs of locomotion and ingestion of food, 

 or for one or the other purpose. Contour of the body stable, sometimes 

 amoeboid, and then for the most part only in the last stage of the life- 

 history. The cilia, flagella, and vibratile membranes are stable structures 

 but retractile under certain conditions. 



There are three classes, the Acinetaria, Infusoria s. Ciliata, and 

 the Mastigophora. 



CLASS ACINETARIA s. TENTACULIFERA. 



Plegepod Protozoa with cilia confined to the bud or fission-product, and 

 to a temporarily assumed motile phase. Fixed as a rule, and provided with 

 prehensile tentacles of one or of two kinds. Rarely naked ; a soft cuticle 

 generally present or a re sis tent lorica. The nucleus is single, occasionally 

 ramified. There are one or more contractile vacuoles, sometimes provided 



