CILIATA 773 



In the ciliated Infusoria, the differentiation of the sareodic sub- 

 stance into ' ectosarc ' or cell-wall, and ' endosarc ' or cell-contents, 

 becomes very complete, the ectosarc possessing a membranous 

 firmness which prevents it from readily yielding to pressure, and 

 having a definite internal limit, instead of graduating insensibly 

 (as in rhizopods) into the protoplasmic layer which lines it. A 

 ' nucleus ' seems always present, being sometimes ' parietal ' (or 

 adherent to the interior of the ectosarc), in other cases lying in the 

 midst of the endosarc. In many Ciliata a distinct ' cuticle ' or 

 exudation-layer may be recognisecl on the surface of the ectosarc: 

 and this cuticle, which is studded with regularly arranged markings 

 like those of Diatomacese, seems to be the representative of the 

 carapace of Arcella c. as of the cellulose coat of protophytes. 

 It is sometimes hardened, so as to form a ' shield ' that protects 

 the body on one side only, or a ' lorica ' that completely invests 

 it ; and there are other cases in which it is so prolonged and 

 doubled upon itself as to form a sheath resembling the ' cell ' of a 

 zoophyte, within which the body of the animalcule lies loosely, being 

 attached only by a stalk at the bottom of the case, and being able 

 either to project itself from the outlet or to retract itself into the 

 interior. In the marine forms known as Dictocysta, and in Codonella, 

 described by Haeckel, the body is enclosed in a silicious lattice-work 

 shell, usually bell-shaped or helmet-shaped, which bears so strong 

 a resemblance to the shells of many Radiolaria as to be easily mis- 

 taken for them. The form of the body is usually much more 

 definite than that of the naked rhizopods, each species having its 

 characteristic shape, which is only departed from, for the most part, 

 when the animalcule is subjected to preSvSure from without, or when 

 its cavity has been distended by the ingestion of any substance 

 alxwe the ordinary size. The cilia and other mobile appendages of 

 the body are extensions of the outer layer of the ' ectosarc ' proper ; 

 and this layer, which retains a high degree of vital activity, is some- 

 times designated the ' cilia-layer.' Beneath this is a layer in which 

 (or in certain bands of which) regular, parallel, fine strife may be 

 distinguished, and as this striation is also distinguishable in the 

 eminently contractile foot-stalk of Vorticella 1 (fig. 593, B) there seems 

 good reason to regard it as indicating a special modification of proto- 

 plasmic substance, which resembles muscle in its endowments. 

 Hence this is termed the * myophan-layer.' Beneath this, in cer- 

 tain species of Infusoria, there is found a thin stratum of condensed 

 protoplasm, including minute 'trichocysts,' which resemble in 

 miniature the ' thread-cells ' of zoophytes ; and this, where it 

 exists, is known as the ' trichocyst-layer.' The hair-like pro- 

 cesses of protoplasm may be caused to protrude from the cell 

 by such irritation as is effected by the addition of a little iodine to 

 the water in which the animalcule is living. 



The vibration of ciliary filaments, which are either disposed 

 along the entire margin of the body, as well as around the oral 



1 On the morphology of the Vorticellinse see Biitschli, MorphoJ. Jahrb. xi. 

 p. 553. 



