226 Dr. C. F. J. Lachinarm on the Organization of Infusoria. 



to arise from very different things being confounded together. 

 The swelling dilatations of existing vessels are certainly often 

 regarded as such vacuoles, without its being remembered that 

 these dilatations always gradually decrease again, whilst the 

 true vascular centres, the contractile spaces, ..always diminish 

 suddenly in healthy animals. Moreover, in diseased Infusoria, 

 an exudation of a fluid, with which the parenchyma is normally 

 imbued, appears to take place from it even into the cavity of the 

 body, and perhaps into chasms of the parenchyma, as we often 

 see it take place in Infusoria, and many other low Invertebrate 

 animals, on the surface of the body. These sarcode-drops ap- 

 pear to be incapable of even being again absorbed, but their 

 formation always appears to lead, although slowly, to the death 

 of the animal. 



Although we may now assert positively that the contractile 

 space is the centre of a vascular system, which does not consist 

 of chasms formed in the parenchyma by its accidental separation, 

 another and more difficult question concerning its nature re- 

 mains to be cleared up, namely, whether the vessels and the 

 contractile space possess proper walls, or whether they are only 

 regular and constant chasms in the parenchyma, and whether 

 the contractile space is or is not a vesicle. The mode of con- 

 traction, which differs from the other contractile phsenomena of 

 the parenchyma of the body, appears to speak decidedly in 

 favour of the vesicular nature of the contractile space. The 

 circumstance that, before its complete expansion, it frequently 

 appears to be divided into two or three, is not opposed to this, 

 as a vesicle may very well be constricted into two or more parts 

 by the partial contraction of annular portions, or by strictures. 

 Some other facts appear to be in favour of the vesicular nature 

 of the contractile space, such as the phsenomenon presented by 

 Spirostomum ambiguum, already referred to, in which balls of 

 excrement pass to the anus between the contractile space and 

 the outer skin of the animal, and, although often arching the 

 wall of the contractile space into a semiglobular form, yet never 

 break through into it. In Actinophrys, the 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 burst at 

 the moment of greatest expansion, if it were only composed of 

 the gelatinous parenchyma of the body*. 



The behaviour of the contractile vesicle in Actinophrys, also, 

 hardly allows us to suppose that it has an opening outwardly ; 



* See Frey, Hautbedeckungen der wirbellosen Thiere; Von Siebold, 

 Vergl. Anat. ; and especially Claparede, Miiller's Arehiv, 1854, p. 417, 

 translated in the Annals, loc. cit. 



