674 



ORDER PERITRICHA. 



beneath the obliquely set and moderately dilated peristome ; contour when 

 contracted pyriform, with the anterior border lobate ; parenchyma trans- 

 parent, colourless ; cuticular surface smooth, soft and plastic, often puckered ; 

 pedicle slender, four or five times longer than the body. Length without 

 pedicle 1-570" to 1-280". 



HAB. Pond-water, forming social clusters on the roots of Lemn<z and 

 other aquatic plants. 



This species may be abundantly obtained at all seasons of the year under the 

 conditions above indicated. By Ehrenberg it has been identified with the Vorticella 

 convallaria, in part of Linnaeus and O. F. Miiller, and also with the Vorticella nebu- 

 lifera of the last-named authority. On referring, however, to Miiller's original account 

 of the type agreeing in name with the present one, the author finds that it relates 

 to a marine species having a much wider bell-like contour, which has not apparently 

 been since observed. That the title of nebulifera belongs properly to the marine 

 animalcule is evident, though custom has so long associated it with the present 

 fluviatile form, that the introduction of a new title for the distinction of the latter 

 type appears undesirable. As seen under the high magnification of six or eight 

 hundred diameters, the cuticular surface is shown to be finely striate transversely, 

 but it does not exhibit such character with one of two or three hundred only, 

 which is employed for establishing that distinction between the smooth and con- 

 spicuously striate types here adopted as an aid to their specific identification. Full 

 details of the reproductive phenomena of the present species, as elicited by Everts, 

 are embodied in the preceding general account of the genus Vorticella, illustrated 

 by Figs. 32-47 of PI. XXXV. 



Everts' interpretation of the minute histology of the contractile footstalk of 

 Vorticella nebulifera is illustrated by the figures from his drawings reproduced in 

 Figs, i and 2 of the accompanying woodcut. According to this investigator, the 

 central muscle-like cord exhibits, under the moderately high magnification of 600 

 diameters (Fig. i) the aspect of being finely and evenly striate transversely, after the 



FIGS, i and 3. Vorticella nebulifera, Ehr. i. Contracted zooid with at s muscle-like element of the pedicle exhibiting 

 a transversely striated aspect, X 600 (after Everts). 2. Diagrammatic longitudinal section of lower half of the body ; 

 c, cuticle ; s, central muscle-like cord of pedicle continued at m into the myophan layer of the body-wall ; x, its 

 central cavity; r, cortical layer; i, central cavity of the body; , nucleus or endoplast, X 1800 (after Everts). 



FIG. 3. Carchesium polypinum, Lin. sp. Portion of stem as observed by the author ; a, external sheath or cuticle ; 

 b, central contractile cord, with c its granular sarcolemma-like investing membrane, which has become exposed and 

 twisted on itself through the fracture and shrinking of the central cord, X 2000. 



manner of the striated muscular fibre of an ordinary metazoic organism. Under the 

 yet higher amplification of 1800 diameters (Fig. 2) each of these apparent transverse 

 striae, however, became resolved into parallel rows of minute longitudinal striae, 



