OF THE PEOTOZOA. CILIATA. 305 



tube behind it and by the primary impetus given it by the action of the cilia ; 

 thus, the more rapidly it is propelled, the greater is the cii'cuit it describes. 

 Stein represents it to make a wide spiral cui've of one or two gyrations in 

 Opercularia, and in 0. herherina to escape finally by a determinate discharg- 

 ing orifice situated at the bottom of the vestibule. In this latter species, he 

 moreover describes the impetus of the swallowed portion to be so strong as 

 to drive the nucleus from its usual position. Although a discharging orifice 

 in a particular site is thus refen^ed to by Stein in the Opercularia herherina, 

 yet at another page (p. 17) he says, generally, that he has been unable to de- 

 tect such a fixed vent in any animalcule, but that where the excreted matters 

 do not, as in Chilodon and other species, escape by the mouth, they make 

 their way to one particular region of the body, through which they escape, 

 not by an opening with a visible margin, but through a rupture of the in- 

 tegument, which closes up and disappears immediately after their exit. 



This production of a fortuitous opening for the escape of the excreta, had 

 been previously described by Dujardin as general in the Ciliata, Siebold, on 

 the contrary, upheld the opposite opinion of the existence of a defined anal 

 aperture among them. In most Stomatoda, the anus (he writes) is generally 

 situated at the opposite extremity of the body to the mouth, and on the imder 

 surface ; but where it is absent, the mouth serves both as inlet and outlet, as 

 among the Polypes. Cohn admits, at least in certain cases, the presence of a 

 definite anus ; for in his recent figures of Nassida elegans {Zeitschr., 1858) 

 he indicates such an aperture (XXYIII. 11^). Lachmann is very positive 

 on this question. He states {op. cit. p. 127) that " a long and careful ob- 

 sei-vation of an individual will always show that the faeces are invariably 

 thrown out at the same part of the body ; and in many Infusoria we may 

 frequently recognize the anus in the form of a smaU pit on the surface of the 

 animal, even for a considerable time before and after excretion (this is often 

 the case in Paramecium Aurelia, P. Bursaria, and Stentor). That the faeces 

 are not forced through the parenchyma at any point on the suiface of the 

 body, is proved especially by the careful observation of Spirostomum ambi- 

 guum, and some new animals which are to be united with the Stentors in one 

 family. In the former, the anus is situated at the hinder end of the animal ; 

 and close in front of it is the very large contractile vesicle. When fully ex- 

 panded, this vesicle appears to be sun-ounded only by a thin membrane ; but 

 nevertheless we see baUs of excrement, often several at the same time, on 

 different sides of the vesicle, separating the laminae of its apparently simple 

 covering, and forming projections which are often nearly hemispherical both 

 towards the vesicle and the outer surface of the body. If masses of excre- 

 ment do usually penetrate through the parenchyma of the body, we should 

 expect it to be the case here when the tension of this is so great ; we should 

 also expect to see the masses of excrement pass into the contractile space, if 

 it were not a vesicle but only a space in the parenchyma without proper 

 walls. Xeither of these things occurs, however ; the faecal masses are not 

 deposited from the body until they have reached the anus at the hinder ex- 

 tremity of the body. A similar strong expansion of a thin part of the body 

 by faecal masses, without any rupture, is seen, as already mentioned, in some 

 new Stentorina, which are distinguished from the genus Stentor by their 

 having that part of the parenchjTna of the body which bears the ciliarj' 

 spiral and the aniLs (which in aU the Stentorina lies on the dorsal siuface of 

 the body close under the eihary spiral, and not in a common pit vdiYi a mouth) 

 drawn out into a thin process. In one genus, of which I observed two species 

 (one is the VorticeUina ampidla of 0. P. Miiller) in company with E. Clapa- 

 rede on the Norwegian coast, and which I will describe elsewhere, this pro- 



