Dr. C. F. J. Lachmann on the Organisation of Infusoria. 225 



the whole length of the body, and sends branches into its rami- 

 fications : 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 remark- 

 able distinctness in the large Stentor polymorphus (including S. 

 Roeselii and 3Iulleri), 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 

 ciliary disk (fig. 8 k). From it a longitudinal vessel runs 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 expansion of the contractile vesicle, 

 but swell up suddenly like the vessels of the above-mentioned 

 Infusoria during its contraction : at this time the longitudinal 

 vessel usually exhibits considerable dilatations, which, when 

 superficially examined, may easily be taken for independent, 

 disunited cavities (vacuoles). (See figs. 8 and 9; the latter 

 figure shows a diagrammatic section of a part of the posterior 

 extremity of Stentor, in the parenchyma of which the dilatations 

 of the longitudinal vessel are seen on the left side.) The 

 annular vessel exhibits a more uniform lumen ; only two round- 

 ish 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 (fig. 8 o o). Both vessels 

 gradually decrease during the reappearance of the contractile 

 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 Spirostomum ambiguum 

 were first described by Von Siebold*, whilst their existence has 

 been erroneously denied by Eckhardtf. 



As we thus find a vascular system in the StentorsX, and in 

 other Infusoria recognize the parts lying nearest to the centre 

 (the contractile space), sometimes easily and sometimes with 

 difiiculty, 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 par- 

 enchyma of the body (vacuoles of Dujardin), is apparent from 

 its regularity. When it is asserted, in proof of the inconstancy 

 of these vacuoles, that exactly similar ones frequently make 

 their appearance in other parts of the body, this appears to me 



* Vergleichende Anatomie, p. 21. 



t Wiegmann's Arcbiv, 1846, p. 237. 



X In opposition to the opinion that this is a system of seminal canals, 

 the existence of the annular vessel in Stentor may also be taken, in addi- 

 tion to the reasons brought forward by other authors. 



Ann. ^ Mag. N. Hist. Ser. 2. 'Vol. xix. 15 



