318 GENERAL HISTORY OF THE INFUSORIA. 



which swelled up when the above-mentioned process became enlarged in con- 

 sequence of the contraction of the vesicle. 



" In Dendrosoma radians (Ehr.), a fine vessel runs through the whole 

 length of the body, and sends branches into its ramifications : it is furnished 

 with a number of contractile spaces, partly in the stem and partly in the 

 branches. 



'' The processes of the contractile space are seen with remarkable distinct- 

 ness in the large Stentoi' polymori^hus (including^. RoeseUi and S. Miilleri), in 

 which a very considerable portion of a vascular system may be recognized. 

 The large contractile space lies a little to the left of the oesophagus, near the 

 plane of the ciliaiy disk. From it a longitudinal vessel nms to the posterior 

 extremity of the animal, and an annular vessel round the ciliary disk (Stirn) 

 close under its series of cilia. Both these are visible even during the expan- 

 sion of the contractile vesicle, but swell up suddenly like the vessels of the 

 above-mentioned Infusoria during its contraction : at this time the longitu- 

 dinal vessel usually exhibits considerable dilatations, which, when superfi- 

 cially examined, may easily be taken for independent, disunited cavities 

 (vacuoles). The annular vessel exhibits a more uniform lumen ; only two 

 roundish dilatations make their appearance in it — one close to the anus on the 

 dorsal side of the animal, and the other close to the oesophagus on the ventral 

 surface. Both vessels gradually decrease during the reappearance of the con- 

 tractile vesicle, apparently without any contraction of their own, in the same 

 way as the vessels of the Paramecia. The longitudinal vessel of the Stentors, 

 and a similar one in Spirostomxmi ambiguum, were first described by Von Sie- 

 bold, whilst theii' existence has been erroneously denied by Eckhard. 



"' As we thus find a vascular system in the Stentors, and in other Infusoria 

 recognize the parts lying nearest to the centre (the contractile space) some- 

 times easily and sometimes with difficulty, we may certainly conclude that 

 such a system exists in all Infusoria which possess a contractile space, even 

 when no branches have been detected running out from this. That this 

 system does not merely consist of accidental chasms in the parenchyma of the 

 body (vacuoles of Dujardin), is apparent fi'om its regularity. When it is as- 

 serted, in proof of the inconstancy of these vacuoles, that exactly similar ones 

 frequently make theii' appearance in other parts of the body, this appears to 

 me to arise from very different things being confounded together. The swell- 

 ing dilatations of existing vessels are certainly often regarded as such vacu- 

 oles, 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 suiface of the body. These sarcode-drops 

 appear to be incapable of ever being again absorbed ; but their formation 

 always appears to lead, although slowly, to the death of the animal." 



After the above details, Lachmann inquires the nature of the fimction this 

 vascular apparatus performs ; and having satisfied himself of the nonexistence 

 of a communication between the interior of the vesicle and the external sur- 

 face, he rejects the idea of its being a water-vascular system, as " we do not 

 possess the certain proof of one of the most essential requii-ements of a water- 

 vascular system — the existence of an external orifice, — and some things 

 appear directly opposed to it." 



Mr. Carter coincides with Lachmann in many particulars respecting the 

 structure of the vascular system of Ciliata ; but in others he materially differs : 



