SYSTEMATIC SURVEY. 105 



Examples. Mastigamceba, possessing a flagellum and amoeboid pro- 

 cesses ; Euglena, very common in wayside pools, with green or variable 

 colouring matter, probably feeding for the most part like a plant ; the 

 colonial Volvox ; Codosiga, with stalked colonies, each individual with 

 a collar round the base of the flagellum ; Proterospongia, colonial, like 

 a detached piece of sponge. Many, e.g. , Monads, live parasitically or in 

 putrid liquids. 



10. DINOFLAGELLATA, very successful Protozoa, which combine 

 activity and passivity, having two flagella and generally a cellulose 

 coat. The one flagellum projects from a longitudinal groove, the other 

 lies in a transverse groove. Mostly marine. 



Examples. Peridininm and Ceratium. 



11. RHYNCHOFLAGELLATA, large forms, with firm rind and very 

 spongy protoplasm, with two flagella, the larger one striated like a 

 muscle, springing from a deep groove, the smaller one near the aperture 

 for the food. 



Examples. The phosphorescent Noctiluca ; Leptodiscus medusoides, 

 disc-like in form, swimming like a miniature medusoid. 



12. CILIATA, provided with numerous cilia, which bend and straighten 

 rapidly, driving the animals along or wafting food particles into the 

 " mouth." There is a definite rind. Beside the large macronucleus 

 there is in most a micronucleus or "paranucleus." There are usually 

 two contractile vacuoles. Multiplication by rapidly succeeding divisions ; 

 in rare cases spores seem to be formed. Conjugation has in some cases 

 at least been shown to be associated with intimate interchange of micro - 

 nuclear material. Parasitic forms, some mouthless, are not uncommon. 



Examples. (a) Peritricha, with a circle of cilia at one end or at 

 both, e.g., Vorticella ; Trichodina, common on Hydra; (b) Hetero- 

 tricha, with long and short cilia, e.g. , the large Stentor, about -^V^h inch 

 in length ; Balantidium coli, in colon of man. (c) Holotricha, uni- 

 formly ciliated, e.g. , Paramcecium ; Opalina, in intestine of frog, with 

 numerous nuclei, and no contractile vacuoles. (d] Hypotricha, locomotor 

 cilia confined to under surface, e.g., Stylonichia. 



13. ACINETARIA, ciliated when young, and probably derived from the 

 Ciliata, but more passive when adult. They are fixed in adult life, 

 generally stalked, and bear tentacle-like processes often suctorial. The 

 nucleus is sometimes branched. They have one or more contractile 

 vacuoles. They multiply by division, or by the formation of buds which 

 usually remain for a time partly enclosed by the parent. Their food 

 consists of other Protozoa. They represent " an extreme modification 

 of the Protozoon series, in which the differentiation of parts in a uni- 

 cellular animal reaches its highest point" (Lankester). 



Examples. Adneta, suctorial ; Dendrosoma, forming branched 

 colonies, suctorial ; Ophryodendron^ non-suctorial. While most Acinetse 

 seize other Infusorians by means of their suckers, there are others of 

 minute size, e.g., Sphcerophrya paramtxdorum^ which penetrate into 

 their prey and become parasites. 



History. Of animals so small and delicate as Protozoa, we do not 

 expect to find distinct relics in the much battered ancient rocks. But 

 there are hints of Foraminifer shells even in the Cambrian ; more than 

 hints in the Silurian and Devonian ; and an abundant representation in 



