Natural History of the Vorticellse. 197 



distinctly perceptible furrow into the reverted seam of the 

 peristome (Pis. XV. & XVI.). 



The body of the Vorticellee usually exhibits towards the 

 middle a bellied protuberance, the anterior part being con- 

 stricted behind the peristome, whilst the posterior end tapers 

 rapidly into a wedge-shaped point. In this case the form is 

 short and stout ; but in other species the body appears elon- 

 gated and without any perceptible swelling in the middle, 

 gradually narrowing backwards from the Avide, open, reverted 

 margin of the peristome, like a tall cup or a champagne-glass. 

 Between these two extremes, however, leaving out of con- 

 sideration the changes of form produced in the same individual 

 by the different states of contraction, we find the most multi- 

 farious transitions, sometimes most nearly approaching the 

 bellied bell-shape, sometimes the elongated funnel-shape. 



The characters of form here referred to, and the denomina- 

 tions of bells, funnels, cups, &c. adopted for them, of com-se 

 apply only so long as the animalcules have unfolded their 

 rotatory organ and peristome. When the ciliated disk is 

 retracted within the body, the peristome, which was previously 

 reverted outwards, lays itself like a cover over the'/ormer, con- 

 sequently covering the whole anterior part of the body. This 

 cover, then, in form and destination completely resembles a 

 muscular sphincter, which, moreover, acquires a radiated 

 appearance by means of the folds of the peristome and the 

 cilia lying beneath it (PI. XII, fig. 1 &c., PI. XIII. fig. 4, 

 PI. XIV. fig. 6, PI. XV, fig. 1 &c.). In these cases, of 

 course, the form of the body is not like that of a bell or funnel, 

 but clavate, pyriform, or even spherical. 



Of the known Vorticellge, only two genera appear to possess 

 freedom of locomotion, namely Astylozoon and Gerda ; the 

 latter, however, which seems to have been as yet very im- 

 perfectly investigated, is limited in this faculty, or rather in the 

 habit of constant free locomotion, as the members of this genus 

 are characterized by Clapar^de and Lachmann as " Vorticellines 

 sessiles," although in them a true adherent organ is entirely 

 deficient. The other Vorticellge are all fixed, either seated upon 

 attached peduncles {Vorttcella, Carchesium, Epistylis^ Zoo- 

 thamnium)^ or non-pedunculate and attaching themselves as 

 parasites upon the soft surfaces of animals (Mollusca) by 

 means of an organ like a sucking-disk at the posterior ex- 

 tremity of the body. The pedunculate Voj-ticellce either sit 

 singly upon simple stalks* (which in this case are always 



* We here follow, for the present, the systematic arrangement of Stein, 

 who, as already explained, has excluded from the Vorticellinse the Ophry- 

 dinae, among which we certainly meet with simple forms with rigid 

 peduncles (e. g. Cothurnia). 



