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CONTRACTILE VESICLES. 69shadowed. Among these latter, reference may be made more especiallyto such types as Anthophysa vegetans and Oikomonas obliquus, in both ofwhich the excrementitious particles are rejected at the posterior regionof the body, and are in the former instance intimately interwoven with thesubstance of the branching stem. Even among the Ciliata, where thisorgan attains its most pronounced development, it is, except during thepassage of rejectamenta, rarely conspicuous. An exception to the aboverule is, however, afforded by the members of the genus Nyctotherus, whereit ispermanently recognizable as a posteriorly located thick-walled,tubular passage, that penetrates to a considerable distance into the substanceof the body. As pointed out by Professor Huxley, * the tractalong which the food passesin this Infusorium is so circumscribedthrough the delimitation of the pharynx, anal passage, and very shortintermediate area of fine granular endosarc or endoplasm, that it may benot inappropriately described as possessing a rudimentary intestinal canal.In common with Nyctotherus, the anal orifice is more usually terminal orsubterminal, but may, as in Stentor or Follicularia, have a lateral location,or as in the large group of the Vorticellidae, itmay open upon theanterior extremity in close vicinity to the oral aperture.Contractile Vacuole or Vesicle.In close association with the anal or excretory aperture the functionsof which it in many instances would seem to assist in performing hasto be described that early recognized organ, sometimes single and sometimesmultiple, presenting in the generality of species the aspect of aclear, rhythmically expanding and 'contracting spheroidal space, mostgenerally distinguished by the title of the " contractile vesicle." A veryconsiderable diversity of opinion has been, and is even yet, maintainedwith relation to the true structure and function of this very importantorgan. By Ehrenberg it was first described as a spermatic gland ;Spallanzani and Dujardin attributed to it a respiratory function ;Lieberkuhnand Claparede and Lachmann recognized in it a rudimentary heartor circulatory organ ;while in accordance with the views of Stein andOscar Schmidt, the functions discharged by it are excretory and correspondmost nearly with that of the renal organ of the higher animals, and theexcretory water-canals of the Turbellaria. As maintained more recentlyby Professor Haeckel, it seems, however, most reasonable to infer that thefunctions performed by the contractile vesicle of the Infusoria partake ofa twofold character, being both respiratory and excretory. One of the mostimportant points for consideration in the determination of the functionsof this organ, is the long-disputed question as to whether or not it maintainsa free communication with the outer water. By the majority ofearlier and many recent writers, including among the latter Claparede* 'Invertebrate Anatomy,' p. 105.