72 ORGANIZATION OF THE INFUSORIA. 



tubular, canal-like diverticulum extends, inferiorly, down the left side of the 

 animalcule to within a short distance of the adherent foot ; while another 

 similar 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 configura- 

 tion of the contractile vesicle occurs in Ophrydium versatile, an anterior 

 annular canal without the posterior diverticulum obtaining also in several 

 other Vorticellidae. Among the numerous examples in which the contractile 

 vesicle takes the form of a simple lateral canal-like prolongation, exhibiting 

 the normal spheroidal dilatation at its point of discharge, with occasionally 

 one or more minor bulbous dilatations at various portions of its course, 

 may be mentioned more especially such genera as Spirostomum, LoxopJiyl- 

 lum, and Climacostomum. In a yet more considerable assemblage of species 

 the contractile vesicular system is remarkable for what may be denominated 

 its dispersed type of representation. With these, instead of presenting a 

 simple, well-defined centre, with perhaps one or more associated canal- 

 like diverticula, a variable and often indefinite number of similar indepen- 

 dently pulsating vacuoles are developed at various separate points. It is 

 thus that in Paramecimn and Panophrys two such separated pulsating 

 centres occur ; in Chilodon, Chlamydodon, and many Acinetidae, simple 

 spheroidal contractile vacuoles, varying in number from three or four 

 only to as many as twenty, are variously and mostly irregularly distributed 

 throughout the cortical substance ; while in a few rarer instances, such as 

 Bursaria truncatella, Trachelius ovum, and the Prorodon margaritifera of 

 Claparede and Lachmann, these independent contractile centres are so 

 abundant as to be almost past enumeration. One other characteristic 

 modification of the compound contractile vacuolar system is exemplified 

 by AmpJiileptus gigas and certain Opalinidae, in which an even serial or 

 linear distribution of these vesiculae is exhibited. In all the examples 

 above cited the animalcules named belong to the Ciliate section of the 

 infusorial class. A plurality of contractile centres is not unfrequently, 

 however, associated with the representatives of the Flagellata. Examples 

 in connection with this group are yielded by the important order of the 

 Choano-Flagellata, among whose members two or more comparatively 

 large posteriorly located contractile vesicles are almost invariably pre- 

 sented, while in certain species of Oikomonas and Anisonema, two equal- 

 sized and in the former case alternately pulsating vacuoles have been 

 observed by the present author. In Anisonema acinus and Entosiphon 

 sulcatum, Stein, again, has indicated in his recently published volume 

 that the normally single and subspheroidal contractile vesicle develops, at 

 diastole, lobate peripheral sinuses, which impart to the entire structure a 

 rosette-like aspect resembling that already referred to in connection with 

 various Ciliata. 



Such being the most prominent external configurations of the contractile 

 vesicle, in both its simple and compound type of development, it yet remains 



