296 GENERAL HISTOEY OF THE INFTJSOEIA. 



In Opercularia, on the contrary, the peristom is neither ciliated, expanded, 

 nor everted in a campamilate manner, but, by the tapering of the anterior 

 thii'd of the body, is narrow (XXX. 1, 37), and frequently throT\Ti into longi- 

 tudinal rugae, and withal simply truncate. Further, the disk has a fiat 

 sui'face, and is supported on a long stem which tapers internally to a fine 

 extremity ; and the whole organ assumes a ti^nmpet-like figure (XXX. 1 «, 

 2 a, d). Moreover, instead of an infundibuliform fissure conducting to an 

 oral aperture or entrance to the ahmentary canal, there is a wide throat or 

 pharjTix, occupying almost the whole diameter of the peristom, having its 

 border extended upwards in the form of a free edge (XXX. 2, 3), which 

 Stein calls an under lip, in contradistinction to the rotary disk, which Ehi-en- 

 berg represented to be a forehead and upper lip. 



The tapering stem of the disk bounds one side (the upper) of the pharynx, 

 and by its narrow extremity communicates with the general cavity of the 

 body. The flat disk itseK is surrounded by two or three concentric rows of 

 long cilia, and when di^awn inwards suffices, with little aid from the constric- 

 tion of the peristom, to close that opening. When, however, contraction is 

 more forcible and complete, this process is entirely retracted, and the peristom 

 closed above it (XXX. 37). When in this condition — and this Is true also of 

 the other allied genera, — the only indication, as before mentioned, of the 

 ciliary apparatus of the head is an irregularly-shaped streak or space, in 

 which cilia may still be discerned. This irregular space is nothing more 

 than the remnant of the pharjTigeal cavity not occupied by the retracted 

 organs. 



On the retraction of the rotaiy disk a portion of its contents is transfeiTcd 

 from the expanded free extremity into its stem, the quantity so removed being 

 in dii^ect ratio with the degree of contraction ; when this is considerable the 

 trumpet-like process appears like a mere internal lobe (XXX. 37 b, li). 



In Lagenoplirys the peristom is pecuhar in being adherent to the narrow 

 two-hpped aperture of the sheath ; the diameter of the two orifices is 

 consequently equal. Prom the peristom a long tnimpet-shaped rotary organ 

 projects, similar to that of Opercularia (XXX. 29, 32, 33, 34). 



The most suigular conformation of the head occurs in a new member of 

 the VorticeUina, described and figiu^ed in Steiu's admii^able monograi^h (p. 205) 

 under the name of Spirocliona (XXX. 17, 27, 28). In this the ordinary struc- 

 ture of the head is entirely departed fi'om ; and we have in its place a con- 

 voluted spii^al membrane or lamella, rolled inwards around a sohd central 

 axis, forming a sort of exaggeration of the single spiral wreath of Stentor. 

 In full-grown specimens of Sjjir. gemmipara, two complete cii'cuits (XXX. 

 17) are made by the lamella, each of which is morphologically the same as 

 the ciliated peristom expanded and flattened out. The suifacc is clothed 

 -svith ciha ; and at its termination in the body, near the axis of the spu^al, is 

 placed the mouth, into which foreign substances are rapidly transmitted by 

 the action of the cilia. 



Among the several members of the families j^assed in review, we have seen 

 a considerable range in the complexity of the cihary ^vreath ; and on extending 

 our examination to other genera, intermediate gradations in structiu'e may 

 be discovered. Thus, through the simj)le spirally- ciu'ved wreath of Stentor 

 (^XXIX. 7), we have a connecting link between Vorticella, on the one hand, and 

 several genera, of which, in respect of the cihary armature of the head, 

 TricJiodina may be taken as the representative. 



Chcetospira, a new genus instituted by Lachmann (A. N. U. 1857, xix.), 

 has a ciliary apparatus so abnormal and peculiar, that it would seem rather a 

 representative of another family than one of the VorticeUina. The anterior 



