96 THE ANATOMY OF INVERTEBRATED ANIMALS. 



cilia, and surround themselves with a structureless cyst. Each 

 encysted Colpoda then divides into two, four, or more por- 

 tions, which assume the adult form and escape from the cysts 

 to resume an active existence. 



Allman has described the encvstment of a Vorticellidan, 

 followed by division of the nucleus into many germs, with- 

 out any antecedent process of conjugation ; and Everts has 

 observed that the progeny of an encysted Vorticella take on 

 the form of Trichodina grandinella. The Trichodince mul- 

 tiply by transverse divisions, and then grow into Vorti- 

 cellce. 1 



Encystment, whether followed or not by division, is very 

 common among all the Ciliata, and a species of Amphilep- 

 tus has been seen to swallow — or rather envelop — a stalked 

 bell-animalcule ( Vorticella), and then become encysted upon 

 the stalk of its prey, just as Vampyrella becomes perched 

 upon the stalk of the devoured Gomphonema. 



In the higher Ciliata, the protoplasm of the body becomes 

 directly differentiated into various structures, in the same 

 way as has already been seen to be the case in Gregarina 

 gigantea, but to a much greater degree. 



Thus, in the Peritricha, of which the bell-animalcules, or 

 Vorticellce (Fig. 9, A, _Z?, C), are the commonest examples, 

 the oral region presents a depression, the vestibule (Fig. 9, a) 

 from which a permanent oesophageal canal leads into the soft 

 and semi-fluid endosarc, where it terminates abruptly ; and 

 immediately beneath the mouth, in the vestibule, there is an 

 anal region which gives exit to the refuse of digestion, but 

 presents an opening only when fecal matters are passing 

 out. Except where the ciliated circlet, or rather spiral, is 

 situated, the outer wall of the body gives rise to a relatively 

 dense cuticula, and not unfrequently secretes a transparent 

 cup or case, foreshadowing the theca of hydrozoal polyps. 

 Moreover, in the permanently fixed Vorticellce, the stalk of 

 attachment may present a central muscular fibre (Fig. 9,/*), 

 by the sudden contraction of which the body is retracted, 

 the stalk being at the same time thrown into a spiral. In 

 the holotrichous Paramceciiim (Fig. 10) beneath the thin su- 

 perficial transparent cuticle from which the cilia proceed, 

 there is a very distinct cortical layer, fibrillated in a direc- 

 tion perpendicular to the surface, and, in some species of this 

 or other genera, as Strombidium and Polykricos (Butschli), 

 beset with minute rod-like bodies similarly disposed, which, 



Allman, " Presidential Address to the Linnsean Society," 1875. 



