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72 ORGANIZATION OF THE INFUSORIA.tubular, canal-like diverticulum extends, inferiorly, down the left side of theanimalcule to within a short distance of the adherent foot ;while anothersimilar canal, departing from the superior region of the same vacuole,extends in an annular form round the entire circumference of the peristome.As recently demonstrated by Wrzesniowski, an almost identical configurationof the contractile vesicle occurs in Ophrydium versatile, an anteriorannular canal without the posterior diverticulum obtaining also in severalother Vorticellidae. Among the numerous examples in which the contractilevesicle takes the form of a simple lateral canal-like prolongation, exhibitingthe normal spheroidal dilatation at its point of discharge, with occasionallyone or more minor bulbous dilatations at various portions of its course,may be mentioned more especially such genera as Spirostomum, LoxopJiyllum,and Climacostomum. In a yet more considerable assemblage of speciesthe contractile vesicular system is remarkable for what may be denominatedits dispersed type of representation. With these, instead of presenting asimple, well-defined centre, with perhapsone or more associated canallikediverticula, a variable and often indefinite number of similar independentlypulsating vacuoles are developed at various separate points. It isthus that in Paramecimn and Panophrys two such separated pulsatingcentres occur ;in Chilodon, Chlamydodon, and many Acinetidae, simplespheroidal contractile vacuoles, varying in number from three or fouronly to as many as twenty, are variously and mostly irregularly distributedthroughout the cortical substance while in a few rarer; instances, such asBursaria truncatella, Trachelius ovum, and the Prorodon margaritifera ofClaparede and Lachmann, these independent contractile centres are soabundant as to be almost past enumeration. One other characteristicmodification of the compound contractile vacuolar system is exemplifiedby AmpJiileptus gigas and certain Opalinidae, in which an even serial orlinear distribution of these vesiculae is exhibited. In all the examplesabove cited the animalcules named belong to the Ciliate section of theinfusorial class. A plurality of contractile centres is not unfrequently,however, associated with the representatives of the Flagellata. Examplesin connection with this group are yielded by the important order of theChoano-Flagellata, among whose members two or more comparativelylarge posteriorly located contractile vesicles are almost invariably presented,while in certain species of Oikomonas and Anisonema, two equalsizedand in the former case alternately pulsating vacuoles have beenobserved by the present author. In Anisonema acinus and Entosiphonsulcatum, Stein, again, has indicated in his recently published volumethat the normally single and subspheroidal contractile vesicle develops, atdiastole, lobate peripheral sinuses, which impart to the entire structure arosette-like aspect resembling that already referred to in connection withvarious Ciliata.Such being the most prominent external configurations of the contractilevesicle, in both its simple and compound type of development, it yet remains