736 ORDER PERITRICHA. 



form, united to each other by a slender, even, dichotomously branching, 

 thread-like pedicle. Length of extended bodies 1-80" to 1-35". 

 HAB. Salt and fresh water. 



Ophrydium versatile is a species remarkable for the very considerable dimensions 

 attained by its social colonies ; while the more normal size of these colonial aggre- 

 gates may be compared with that of a walnut, it not unfrequently happens that old 

 established stocks present an almost spherical contour with a diameter of no less than 

 five inches. The number of united zooids in these larger colonies must be reckoned 

 at least by millions, and when drifting upon the surface of the water they bear so 

 close a resemblance to similarly shaped detached masses of the fresh-water sponge, 

 Spongilla lacustris, that without a nearer examination they may easily be mistaken 

 for that organism. Although a type that has attracted the notice of all the earlier 

 and most modern writers it being identical with the Vortlcella versatilis of Miiller, 

 and probably also the Ulva and Tremella pruniformis of Linnaeus it is but quite 

 recently that an exhaustive and accurate account of its more minute anatomy has 

 been placed on record. This has been contributed by Professor A. Wrzesniowski 

 to the number of the ' Zeitschrift fur Wissenschaftliche Zoologie,' Bd. xxix. Heft. 3, 

 1877, containing the results of his investigation of Dendrocometes paradoxus and 

 other infusorial types already alluded to. Previously it had been represented by 

 the chief authorities, including even Stein, that the adjacent animalcules were quite 

 independent of one another, and simply immersed within or adherent posteriorly 

 to the peripheral layer of their common gelatinous matrix. By Fresenius, never- 

 theless, so long since as the year 1849, ^ was reported that an independent thread- 

 like stalk was produced from the posterior termination of each zooid and penetrated 

 nearly to the centre of this matrix, but this observation was not confirmed by sub- 

 sequent investigation. As now shown, however, by Wrzesniowski, such a thread-like 

 stalk is not only possessed by each animalcule, but all of these stalks are united in a 

 dichotomous manner to one another, and form in the aggregate a symmetrical 

 bifurcating thread-like pedicle comparable to that of an Epistylis, and produced in a 

 like manner by the repeated longitudinal fission and centrifugal outgrowth of the' 

 primary zooids. The common gelatinous matrix within which the whole of this 

 branching pedicle is immersed has also been more generally represented as forming a 

 single, continuous, homogeneous investment, but the authority quoted has shown that 

 by treatment with osmic acid this element is resolvable into distinct subcylindrical 

 areas, each representing the portion formed by a separate individual, and having 

 at its latest produced or distal region an ovate cavity, resembling that of the lorica 

 of a Cothurnia or Vaginicola ; it is within this cavity that the animalcule is found in its 

 contracted state after treatment with the reagent named. Illustrations of this matrix 

 thus treated and of the branching pedicle, reproduced from Wrzesniowski's delineations, 

 will be found in Figs. 4 and 8 of the accompanying plate. In addition to the more 

 ordinary green form of this animalcule Wrzesniowski obtained another in which 

 the colouring matter was entirely absent. Upon this he has proposed to confer the 

 title of Ophrydium versatile var. hyalinum, retaining that of O. versatile var. viride 

 for the more normal coloured type. This hyaline variety is shown, however, to differ 

 in so many other more important points that the author is inclined to regard it as 

 a distinct species identical probably with the form next described. Among the chief 

 distinctions cited may be mentioned more especially the considerably smaller size of 

 the zooids, which never attain to one-half of that of the coloured ones, and are only 

 found inhabiting small attached gelatinous matrices of but a few millimetres' diameter, 

 while their supporting stalks are simple or but slightly branched. It was further 

 observed that the stalk in the green variety, immediately beneath its juncture with 

 the body, exhibited frequently three or four prominent annulations, which were 

 never detected in the hyaline form. The phenomena attending the establish- 

 ment of new colonies by these respective varieties or types present likewise 

 an important divergence. The zooids separated from the parent mass of the 

 coloured form attached themselves freely to whatever substance with which they 



