NATURAL HISTORY. 



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and a flagellura also. The fact that the Tentaculifera are totally unlike the other Infusoria in their 

 adult age is very remarkable ; but it is evident that before they attain maturity they resemble 

 the Ciliata. New structures are thus, by evolution, given to the Tentaculifera, and they have 

 considerable affinities with the Rhizopoda. Their adult form is in advance of the ciliate young 



one, and the order Tentaculifera must stand at the 

 head of the Infusoria. Next come the Ciliata, then 

 the Cilio-flagellata, and, finally, the Flagellata. 



The Infusoria are uni-cellular, and this is true 

 where there are two or more individuals in close 

 contact, or where a common stem supports the 

 bodies of others, which may be numerous. For in 

 these instances subdivision of the parent has pro- 

 duced the independent creatures. In the Tenta- 

 culifera, however, the most highly-organised 

 amongst the Infusoria, in the species called 

 Dendrosoma radians (Fig. 6), there is a root com- 

 mon to many trunks which give origin to branchlets 

 terminating in a bundle of tentacles with suckers. 

 This arrangement can hardly be called uni-cellu- 

 lar ; there is, however, no actual cell division, and 

 indeed the ordinary idea of the single cell is hardly 

 applicable to this and many other Infusoria. 



The simplest Infusoria belonging to the Flagel- 

 lata, which have no special spot for the ingestion 

 of food,* have no distinct environing membrane 

 over their soft finely granular protoplasm, and they 

 can assume various shapes for a while. Others 

 belonging to the same group have the outside of the 



body slightly more solid than the rest. In the Ciliata the presence of an outer membrane is evident, 

 and it is possible to distinguish, on some of them, four layers around the soft semi-fluid central 

 eiidoplasm. On the outside is a perfectly transparent structureless membrane, and it is a true cuticle. 

 It forms a sheath for the stalk of some Infusorians, and the covers or shields (lorica) of others 

 (Fig. 7). It is composed of formed material, and is independent of the nutrition of the animal 

 Under the hyaline outer layer there is, without exception amongst the Ciliata, a 

 firm homogeneous elastic and contractile layer, of which the cilia and their various 

 modifications are the offshoots. They penetrate the outer layer and arise from this 

 inner one. In some, but not all, of the Ciliata, there is a layer beneath this last 

 one, which is more or less fibrillar, and highly contractile. It is the muscular, or 

 myophan layer of Haeckel. In the genus Stentor (p. 367) it is highly developed, and 

 it can be seen, by using high and well-defining powers, in the common Vorticella, in 

 which it forms the central, or contractile, part of the stalk, and a thin layer con- 

 tinuous with this is in the body. The fourth layer is not invariably found, but 

 it has been already noticed in the description of a Paramecium. It produces and 

 holds in place the minute rod-like bodies called trichocysts, which will be noticed 

 farther on. These layers constitute the ectoplasm. 



The endoplasm, situated within the ectoplastic or outer layers, is more or less 

 fluid, granular, and coloured glairy protoplasm. It is tolerably immobile in many 

 Infusoria. In most it is subject to amoeboid movements, to a faintly-developed 

 rotatory movement, and to what may be called streaming. In some instances the movement is 

 strong, and resembles that of the cyclosis of plants, as in Yallisneria and Chara. Noctiluca, the 

 phosphorescent flagellate Infusorian, has the endoplasm more or less in the form of a network, 

 with vacuole spaces, and a quantity of granular substance, and this condition is seen in other forms. 



* Group Pantostomata 



Fig. 6. DEXDROSOMA EADIANS. (After SavilleKcnO 



a, Embryos escaping with cilia; 6, buds producing embryos like the 

 parent ; st, stolon. 



Fig. 7. TINTIX- 

 NUS LAGE- 

 NIJLA, SHOW- 

 ING THE 1.0- 

 1UCA AND THE 

 CKOWX OF 



CILIA. 



