738 ORDER PERITRICHA. 



type next described. In no instances was the pedicle branched or even bifurcated, 

 though in some of them nearly double the length of the extended zooid. In 

 O. viride, as described by Wrzesniowski, the ramification of this structure is mani- 

 fested at a very early period, more usually on arriving at a length of one-half or 

 even one-quarter only of that of the animalcule's body. The plasticity of the 

 parenchyma and cuticle in this type would seem to exceed that of either the fore- 

 going or succeeding forms, such plasticity allowing the animalcules to throw 

 themselves into a complicated folded contour as delineated at PI. XLI. Fig. ii^. 

 The increase of this species by transverse fission — a phenomenon of rare occurrence 

 among the VorticellidcE — was noted on numerous occasions, the zooids so multi- 

 plying dividing across the centre, and the ultimately detached anterior half acquiring, 

 a little in advance of this line, an annular zone of locomotive cilia as in the motile 

 zooids of an ordinary VortUrHa. In the last-named type, however, it is the whole 

 animalcule that becomes disconnected, while in the present instance the posterior 

 half is left attached to the pedicle, and developing a new contractile vesicle and 

 oral system, assumes the form of an ordinary zooid. In this process of subdivision 

 the characteristic cord-like endoplast takes its share. The detached portion 

 swims away in a conical form, as delineated at PI. XLI. Fig. 19, and settling down 

 lays the foundation of a new colony, or in some instances coalesces probably with 

 other sedentary animalcules to ensure the sexual rejuvenation of the species. 

 This last phenomenon has not, however, up to the present time been actually 

 observed. 



As a more recent synonym of OpJuydinm EicJiorttii must be included the type 

 figured and described by Dr. H. C. Evarts in the ' American INIonthly Microscopical 

 Journal,' vol, L, 1880, under the title of Ophrydiian Ada;.*- The colony-masses 

 obtained from American waters measured in diameter from one-half to two lines, 

 the larger examples including as many as a thousand zooids. No new data are 

 recorded by Dr. Evarts with reference to their structure or development. 



Oplirydmm sessile, S. K. Pl. XLI. Figs. 19-21. 



Bodies hyaline, colourless or of a slightly brownish hue, attenuate, sub- 

 cylindrical, truncate or tapering posteriorly, sometimes slightly inflated 

 centrally, attached immediately, without the medium of a peduncle, to the 

 fulcrum of support ; the cuticular surface finely annulate transversely ; 

 zooids forming small hemispherical masses of closely approximated indi- 

 viduals not exceeding one-eighth of an inch in diameter. Length of extended 

 bodies 1-80". Hab. — Fresh water, on Anacharis and other aquatic plants. 



This animalcule was received by the author in November 187 1, from Mr. Bolton, 

 in company with the species last described, and of which it was at first regarded as 

 the initial or immature condition. Amongst the points favouring its specific distinct- 

 ness from the type Ophrydium Eic/iornii, it may be mentioned that no examples of 

 this sessile form were found associated with the consignment remitted in the year 

 1874, and that colonies of as many as from forty or fifty to several hundred stalkless 

 individuals have been met with, while in the last-named type the stalks were fully 

 developed in clusters of as few as four zooids. There can be little doubt that this 

 stalkless species of Ophrydium is identical with the animalcule described and some- 

 what roughly delineated by Mr. H. J. Slack in his ' Marvels of Pond Life,' p. 152, 

 ist ed., 1 86 1, and there referred with hesitation to the genus Vaginicola. The zooids 

 in this instance presented, as at first observed and figured, a more evenly cylindrical 

 contour and a more abruptly truncate base than was exhibited by the examples 

 forwarded by Mr. Bolton, while the parenchyma, instead of being white and trans- 

 parent, was tinged a brownish hue. After being kept a day, their bodies were 



See also 'Journal of the Royal Microscopical Society,' April 1880. 



