OF THE PROTOZOA. CILIATA, 317 



doubtful of the stellate structure, as an actual fact, in the Paramecia ; for in 

 P. Bursaria, in Nassida, and other animalcules this apparent structure may- 

 be, he beheves, produced at will by the exercise of slight pressui^e, as by that 

 of the thin glass-cover upon the object, when the diastole of the vesicle is 

 incomplete. Again, he objects against the supposed water-vascular system 

 and its respiratory office, that, in comparison to the large ciliated pharynx, 

 within which a fresh supply of water is perpetually introduced, and through 

 whose dehcate walls a res23iratory act may be readily conceived to take place, 

 the small contractile space commonly appended to it appears of inconsider- 

 able importance as an aerating organ. Further, he cannot conceive the 

 necessity of a respiratory apparatus in any animalcule which lives surrounded 

 on all sides by water, besides receiving it incessantly within its interior, and 

 which can therefore so readily absorb its oxygen through its deKcate tissues. 

 Another fact adverse to this assigned function is, that the vesicles of embryos, 

 whilst stni within the parent, are seen in full activity, although in that posi- 

 tion no renewed supply of fresh water is afforded them. 



These objections of Stein lessen upon consideration : thus his opinion that 

 the vesicle is a mere vacuole, that its radiating canals are probably accidental 

 appearances, and his ignoring the existence of a set of vascular channels 

 through the interior, are set aside by the direct observations of several 

 naturalists to the contrary. So, although his arguments, generally, against 

 the presence of a special respiratory apparatus are not without force, yet the 

 remark that he can conceive no need of such an apparatus in animalcules so 

 cii'cumstanced as the Ciliata is worthless as an argument ; for in all such 

 inquiries into the phenomena of life we are not to suppose an organization 

 and then to find it, but, on the contrary, to discover facts, and then, if possi- 

 ble, to determine on their nature. 



That the contractile vesicle and its connected channels do not constitute a 

 water-vascular and respiratory system, is also the opinion of Lachmann and 

 Carter. The former able observer has confirmed and extended our previous 

 knowledge of the vascular apparatus, and thus conveys his researches and 

 opinions {op. cit. p. 224) : — " When the contractile space (of Pay^mecium 

 Aurelid) is full and ^vide open, the rays can only be observed as fine lines, or, 

 when the light is not good, are entirely imperceptible ; by the sudden con- 

 traction of the space, however, they instantly swell into a pyriform com- 

 mencement close to the position of the contractile vesicle which has disap- 

 peared. "With favoiu-able illumination, when the animals possess the proper 

 degree of transparency, the rays may be traced in Paramecmm Aurelia across 

 the half of the animal, and we may sometimes perceive a bifurcation of one 

 or other of them. During the slow reappearance of the contractile space, 

 the rays gradually decrease ; and they have almost entirely disappeared, or 

 become reduced to fine lines, when the vesicle has attained its fiill extension. 

 These rays, as well as the contractile spaces, lie, as in all Infusoria, close 

 under the skin (' cuticula ' of Cohn), in the parenchyma of the body (' corti- 

 cal layer' or ' cell-membrane ' of Cohn). 



" In many Vortkellce we also find j)rocesses going off from the contractile 

 vesicle (Ehrenberg even states that he has frequently seen the contractile 

 vesicle of Carchesium polypinum lobate or almost radiate) ; of these I have 

 been able to trace one particularly, in V. yiebidifera, V. Campanula, and Carche- 

 sium polypiyium, up to close beneath the skin of the cihary disk ; this, when 

 seen from above, exhibited a longish section. From this a fine branch appears 

 to nm, on the upper wall of the vestibulum, transversely across this to the 

 other side ; at least, I have seen a thin process hanging down like a short 

 curtain into the vestibulum from the side turned towards the ciliary disk. 



