CONTRACTILE VESICLES. 69 



shadowed. Among these latter, reference may be made more especially 

 to such types as Anthophysa vegetans and Oikomonas obliquus, in both of 

 which the excrementitious particles are rejected at the posterior region 

 of the body, and are in the former instance intimately interwoven with the 

 substance of the branching stem. Even among the Ciliata, where this 

 organ attains its most pronounced development, it is, except during the 

 passage of rejectamenta, rarely conspicuous. An exception to the above 

 rule is, however, afforded by the members of the genus Nyctotherus, where 

 it is permanently recognizable as a posteriorly located thick-walled, 

 tubular passage, that penetrates to a considerable distance into the sub- 

 stance of the body. As pointed out by Professor Huxley, * the tract 

 along which the food passes in this Infusorium is so circumscribed 

 through the delimitation of the pharynx, anal passage, and very short 

 intermediate area of fine granular endosarc or endoplasm, that it may be 

 not inappropriately described as possessing a rudimentary intestinal canal. 

 In common with Nyctotherus, the anal orifice is more usually terminal or 

 subterminal, but may, as in Stentor or Follicularia, have a lateral location, 

 or as in the large group of the Vorticellidae, it may open upon the 

 anterior extremity in close vicinity to the oral aperture. 



Contractile Vacuole or Vesicle. 



In close association with the anal or excretory aperture the functions 

 of which it in many instances would seem to assist in performing has 

 to be described that early recognized organ, sometimes single and some- 

 times multiple, presenting in the generality of species the aspect of a 

 clear, rhythmically expanding and 'contracting spheroidal space, most 

 generally distinguished by the title of the " contractile vesicle." A very 

 considerable diversity of opinion has been, and is even yet, maintained 

 with relation to the true structure and function of this very important 

 organ. By Ehrenberg it was first described as a spermatic gland ; 

 Spallanzani and Dujardin attributed to it a respiratory function ; Lieber- 

 kuhn and Claparede and Lachmann recognized in it a rudimentary heart 

 or circulatory organ ; while in accordance with the views of Stein and 

 Oscar Schmidt, the functions discharged by it are excretory and correspond 

 most nearly with that of the renal organ of the higher animals, and the 

 excretory water-canals of the Turbellaria. As maintained more recently 

 by Professor Haeckel, it seems, however, most reasonable to infer that the 

 functions performed by the contractile vesicle of the Infusoria partake of 

 a twofold character, being both respiratory and excretory. One of the most 

 important points for consideration in the determination of the functions 

 of this organ, is the long-disputed question as to whether or not it main- 

 tains a free communication with the outer water. By the majority of 

 earlier and many recent writers, including among the latter Claparede 

 * ' Invertebrate Anatomy,' p. 105. 



