656 ORDER PERITRICHA. 



the apparent gulf between Ophrydium and the more ordinary naked or loricate 

 Vorticellidae is effectually bridged. This last-named genus may, in fact, in accord- 

 ance with the results of Wrzesniowski's and the author's investigations, be regarded 

 as a slime-immersed Epistylis, all the zooids comprising a colony-stock being in a 

 like manner united by a slender branching unretractile pedicle. The elegant tree 

 or shrub-like colonies and variously modified loricae formed by many of the genera 

 of this family have hitherto won for them an amount of interest and popularity 

 possessed perhaps by no other members of the Ciliate group, but, as already shown 

 in the preceding volume, these have now to contend for the palm of beauty with 

 formidable rivals among the humble Flagellata, and wherein, on a comparatively Lilli- 

 putian scale, we find mimetically foreshadowed as many or even more variations of 

 tree or vase-like growths than are embodied in the present more familiar and highly 

 attractive group. As a necessary accompaniment of the combined sedentary and 

 eminently social habits of the majority of the representatives of this family, many of 

 them build up associated colony-stocks of so considerable a size as to form in their 

 natural habitats an appreciable and even conspicuous feature to the unassisted 

 vision. Hence also it is that the Vorticellidae are found to comprise the earliest 

 known of infusorial types, certain of them having been discovered by Leeuwenhoek 

 over two centuries ago, while the typical genus Vorticella lays claim to the illustrious 

 Linnaeus as its founder. 



A moot point concerning the structural features of the Vorticellidae is connected 

 with the apparently long bristle-like appendage frequently seen projecting to a 

 greater or less extent from the vestibular fossa of the various members of this group, 

 to which attention was first directed by Lachmann. This debatable structure, as 

 recognized by various recent investigators, has been usually distinguished by 

 the title of the " sole de Lachmann" first given to it by M. Claparede, but is here 

 more often referred to as the " vestibular seta." A few authorities, on the other 

 hand, and more especially Professor H. James-Clark,* have called in question the 

 existence of such ah appendage, and consider it to be merely the optical image 

 produced by the descending adoral fringe of cilia as seen in profile, or as he puts it, 

 by the intersection of two such rows. In certain instances again see Opercularia 

 stenostoma there can be but little doubt that this so-called organ is rightly the 

 optical outline of a delicate hyaline membrane. In many species of Vorticella and 

 Epistylis, nevertheless, the author is quite satisfied that such a structure exists, quite 

 independent of the adoral cilia, and such a decision is fully supported by the 

 recent investigations of Greeff and Wrzesniowski. The more intimate structure of 

 the pedicle in Vorticella, the typical representative of the family group, is treated of 

 in the account given of that genus, but a few of its more important modifications in 

 other allied genera may be here enumerated. In Carchesium and Zoothamnium it 

 consists similarly of a contractile central cord enclosed within a tubular hyaline 

 sheath, which two elements are respectively homologous with, or indeed attenuate 

 prolongations of, the delicate subcutaneous myophan or muscular layer and 

 superimposed hyaline and structureless cuticle of the zooid's body-wall. In Zoo- 

 thamnium it is noticeable that the basal portion or main trunk of the branching 

 pedicle or zoodendrium is devoid of such an enclosed cord, and therefore non- 

 contractile, and represented by the last only of the two elements just named. This 

 more simple type of structure partly developed in Zoothamnium characterizes the 

 entire extent of the compound pedicle of Epistylis and Opercularia, and also the 

 simpler ones of a numerous host of solitary, short-stalked forms. By Stein it has 

 been maintained that the indurated lorica of Cothurnia, Vaginicola, and their allies is 

 morphologically identical with the pedicle of such forms as Epistylis. In some of 

 these, however, as for example the newly described Pyxicola operculigera, a long sup- 

 porting pedicle is found co-existent with an indurated lorica, this last-named structure 

 being evidently, as with the rigid pedicle, a modification or redundant develop- 

 ment only of the hyaline cuticular layer, the passage of the one to the other being 



* ' Proceedings Boston Society Natural History,' vol. x., 1866. 



