98 THE ANATOMY OF INVERTEBRATED ANIMALS. 



totherus it appears to be confined to a part of the body be- 

 tween the end of the gullet and the anal region, which in 

 this Infusorium is seated at one end of the body. In fact, the 

 finely granular endosarc of Nyctotherus so limits the passage 

 of the food-vacuoles that the tract along which they pass 

 might properly be described as a rudimentary intestinal canal. 



The oral cavity is usually ciliated : sometimes, as in Chilo- 

 don, it has a chitinous armature, which becomes somewhat 

 complicated in Ervilia (Dysteria 1 ) and the Didinium de- 

 scribed by Balbiani. 



Torquatella (Lankester) has a plicated membrane around 

 the mouth in the place of cilia. 



The contractile vacuoles attain their greatest complexity 

 in the Paramcecia, in which there are two — one toward each 

 end of the body. They are lodged in the cortical layer, and, 

 in diastole, a portion of their outer periphery is bounded only 

 by the cuticle, through which it is very probable that they 

 communicate with the exterior. When the systole takes 

 place, a number of fine canals, which radiate from each vac- 

 uole, are seen to become distended with clear, watery fluid. 

 These canals are constant in their position, and some of 

 them may be traced nearly as far as the mouth ; so that the 

 canals and vacuoles form a permanent water-vascular system. 

 The endoplast is finely granular, like the substance of the 

 endosarc. It is frequently said to be enveloped in a distinct 

 membrane, but I am disposed to think that this is always a 

 product of reagents. Attached to one part of it there is very 

 generally (but not in the Vorticellce) a small oval or rounded 

 body, the so-called "nucleolus" or endoplastule. The endo- 

 plast is commonly said to be imbededd in the cortical layer, 

 but this is certainly not the case in Colpoda, Paramcecium, 

 Balantidium, or JVyctotherus. 



The outermost, or cuticular, layer of a large portion of the 

 body becomes hardened and forms a sort of shell, in many of 

 the free Infusoria. In the free marine Dictyocystida and 

 Codonellida of Haeckel, the body has a bell-shaped enve- 

 lope, which in the Dictyocystida (see Fig. 1) is strengthened 

 by a siliceous skeleton like that of a Radiolarian. In both 

 genera the circular lip which surrounds the oral end is pro- 

 vided with numerous long fiagelliform cilia. 2 



Most of the Ciliata, while in full activity, multiply by di- 



1 Huxley, " On Dysteria." ( Quarterly Journal of Microscopical Science, 1857.) 



2 Haeckel, u Zur Morphologie der Tnfusorien," 1873. 



