OF THE PEOTOZOA. CILIATA. 315 



supposition that there is a membranous boundary, at least on the outside of 

 the contractile vesicle, can hardly be rejected, as its wall, which is situated 

 on the outermost surface of the body, must biu-st at the moment of greatest 

 expansion, if it were only composed of the gelatinous parenchyma of the 

 body." 



Still the contrary opinion, viz. that the contractile spaces are mere vacuoles 

 in the substance of the interior, without a limiting membrane, has found able 

 supporters in Meyen, Dujardin, Stein, and Perty. The first-named writer 

 compares them to the changing vacuoles which spontaneously generate in 

 the vegetable protoplasm of plant- cells, by an inherent property or process 

 knoT\Ti as that of vacuolation, and which is equally a phenomenon of simple 

 animal protoplasm or contractile tissue. Indeed, there is no doubt that clear 

 hollow spaces or vacuoles may appear and disappear within the substance of 

 Protozoa, and that some of those remarked by Dujardin, Siebold, and others 

 immediately beneath the integument were of this number ; yet such vacuoles 

 want the constancy in position, figui^e, and pulsating power belonging to true 

 contractile sacs. Besides, as we shall presently see, the evident ramifications 

 or canalicuh of many contractile vesicles among the Cihata afford further 

 groimds for distinguishing between these and mere vacuoles, which, as far as 

 we are aware, never have such offshoots. 



Another questionable point among observers is, whether any communica- 

 tion exists between the cavity of the contractile vesicle and the free surface 

 near to which it is placed. The majority concur in the negative ; but several, 

 among whom are Oscar Schmidt {Froriep^s Notiz., 1849, vol. ix. ; Lehrhuch 

 der Vergleichend. Anatomie, 1853), Mr. Gray {Silliman's Journ. 1853), Mr. 

 Rood (SiUiman''s Journ. 1853, p. 70), and Mr. Carter, are of oj)inion that a 

 du^ect communication, between the fluid contents of the vesicle and the watery 

 medium bathing the external surface, is established by means of foramina in 

 the walls. On this question Lachmann remarks (op. cU. p. 227) — " In many 

 Infusoria we see one or more pale spots upon the contractile vesicle, which 

 may easily be mistaken for orifices, but on closer examination prove to be 

 only thin spots in the parenchyma of the body and the skin, by which the 

 action of the external water upon the contents of the vascular system is 

 certainly facilitated, so that they probably serve for respii'atory purposes. 

 These round clear spots are particularly numerous upon the contractile space 

 of Spirostomum ambiguum.'^ The admission or the denial of such a commu- 

 nication will very much affect the opinion held concerning the nature of the 

 office performed by the vesicle, to which we shaU immediately advert. 



The superficial vesicles or vacuoles before aUuded to, considered by Dujardin 

 of the same nature as the contractile vesicle itself, have not been sufiiciently 

 examined and defined of late to warrant a conclusion as to their real cha- 

 racter : yet probably some of those spaces are no more than mere vacuolae, 

 whilst others are dilatations of the channels of the ramified vascular system. 

 Mr. Carter would in general assign to them the latter character. However, 

 we beheve that many of those which have attracted attention have been 

 isolated vesicles, developed from time time, and to be concerned in securing 

 a more perfect aeration of the contained fluid. Siebold, indeed, went so far 

 as to presume they opened upon the external surface, and brought their con- 

 tents into relation Mdth the surrounding water. 



In figure, contractile spaces are, for the most part, round or somewhat 

 oval, and as to size stand in no direct relation with that of the animalcules 

 they appertain to. Examples of the prevailing figiu^e are seen in Ophrydiimi, 

 Zooihamnium, ChiJodon, Colpoda, Trichodma, &c. Even in some of these appa- 

 rently simple globular sacs, Mr. Carter discovered a series of spherical sinuses 



