7<D ORGANIZATION OF THE INFUSORIA. 



and Lachmann, it has been affirmed that no such intercommunication 

 exists, and that the organ consequently partakes of the character of a 

 closed vessel. Among the first to arrive at a contrary decision and to 

 declare that the contents of this vacuole were at the time of collapse 

 or "systole" discharged externally, may be mentioned the names of 

 Oscar Schmidt and Mr. H. J. Carter, strong confirmatory evidence in 

 the same direction being likewise contributed by Professor E. Ray 

 Lankester, in his " Remarks on Opalina and its Contractile Vesicles," pub- 

 lished in the 'Quarterly Microscopical Journal' for the year 1870. Since 

 that date testimony has been forthcoming from a variety of sources 

 establishing beyond question the existence of the intercommunication 

 above indicated, its precise pore-like character being further described and 

 figured by Wrzesniowski in association with the genera Enchelyodon and 

 Dendrocometes. In the last-named type, furthermore, a delicate tubular 

 canal has been found to proceed from the spheroidal vesicle and to 

 penetrate the thick cuticular investment. A second disputed point, almost 

 equal in its consequence and bearings to the preceding, was for a long while 

 connected with the precise structure of the contractile vesicle, and more 

 especially as to whether or not it possessed a distinct bounding membrane. 

 By Ehrenberg, Siebold, Claparede and Lachmann, and also by Mr. Carter, 

 the presence of such a definite wall or bounding membrane to this vesicle 

 has been maintained ; a contrary view, however, being advocated by Dujardin, 

 Perty, Stein, and the majority of recent investigators. In accordance with 

 the opinion of these latter, no such bounding membrane exists, the vesicle in 

 this respect presenting no higher structural differentiation than the various 

 non-contractile or irregularly contractile vacuoles or lacunae that occur so 

 abundantly in the protoplasmic element of both animal and vegetable 

 cells. The non-possession by the contractile vesicle of any bounding 

 membrane is now amply proved through the tendency exhibited by this 

 structure in certain species to split up into a variable number of minor 

 vesicles, which may again unite in an irregular manner with one another. 

 This phenomenon has been especially demonstrated by Wrzesniowski 

 in connection with the Holotrichous type Trachelophyllum apiculatum. 

 The non-occupation by the contractile vesicle of this species of a perma- 

 nently fixed position has likewise been elicited by this authority, he having 

 observed that during the discharge of faecal matter from the terminal anal 

 aperture the vacuole is forced backwards to a very considerable extent to 

 permit of its free passage. 



The constant and free intercommunication of the contractile vesicle with 

 the outer water or other inhabited fluid medium, and the composition of 

 this structure as a mere rhythmical pulsating vacuole or lacuna in the 

 cortical layer of the ectoplasm, possessing no distinct bounding membrane, 

 being here accepted as fully established, further details with relation to the 

 functions and more prominent variations it assumes in various infusorial 

 types may be proceeded with. In its simplest form, and as represented 



