GENUS TRICHODINA. 



647 



Boston Society of Natural History, vol. i., 1865, and is reprinted in 'Annals of 

 Natural History' for June 1866. Several of the more important structural features 

 elicited through this investigator are reproduced in the accompanying woodcut. 

 According to this authority the elongate dicebox-like contour referred to and 

 reproduced in the figure first cited, represents the normal one maintained by this 

 animalcule in a state of health, the turban-shaped or conical ones given by 

 Stein and other writers being assumed only when in a sickly condition, or when 

 confined within too small a space for perfect freedom of motion. The periphery 

 of the body behind the adoral ciliated disc is described by Professor Clark as exhibit- 

 ing in transverse optical section an exceedingly irregular outline, arising from the 

 fact that the body is fluted and ribbed exteriorly from one end to the other by irregular 



f. y 



Trichodina pediculus, Ehr. i. Diagrammatic illustration of longitudinal optical section. 2. A basal view of the 

 adherent apparatus, velum, and part of the posterior row of cilia, X 950. 3. Two of the uncini with their corresponding 

 radii from the adherent apparatus of a dead specimen X 2000. The lettering is alike throughout : a, anal aperture ; 

 6, vibratory crown ; c, bottom of the cupuliform disc ; d t peristome opposite and beneath the vestibular aperture ; 

 d\, peristome, dorsal region ; d 2, peristome, ventral region ; e, lumen of the edge of the row of vibrating cilia, hitherto 

 supposed to be a distinct vestibular seta ; f, profile of the velum ; fi, free edge of the velum ; _/2, the basal edge or 

 line of attachment of the velum ; g, basal wreath of cilia ; h, hooks or uncini of the adherent organ ; h 2, the spur, and 

 h 3, the horizontal limb of the uncinus ; i, the radii ; i i, the " nail-shaped piece " ; it, its head ; 13, the membranous 

 web ; k, the membranous crest of the uncini ; /, the profile of the " striated membrane " ; / i, its distal edge ; 1 2, the 

 coarser striae as seen on its front face ; 1 3, its proximal edge ; 1 4, 1 5, a portion of the posterior face of the striated 

 membrane showing the finer striae ; nt, entrance to the vestibule ; , nucleus or endoplast ; o, cesophagus ; /, the outer, 

 and / i, the inner walls of the body ; s, general digestive cavity ; v, vestibule. (After Prof. H. James-Clark.) 



longitudinal furrows and projections. At first it was presumed that these rib-like 

 structures were of a muscular nature, but they were ultimately determined to be 

 merely folds and thickenings of the body-wall. The production of the truncate 

 posterior margin of the body as a thin transparent membrane, into the base of 

 which, and on its inner side, the cilia of the posterior fringe are inserted, as estab- 

 lished by Professor Clark, reconciles in a most satisfactory manner the somewhat 

 conflicting accounts of this region given by other observers. By the majority of 

 these the posterior margin is represented as simply fringed with cilia, while by others, 

 including more especially Siebold, it has been reported as consisting solely of a thin, 

 non-ciliate, undulating membrane. Upon the accessory membrane now demonstrated 

 to exist in combination with a fringe of cilia, Professor Clark has proposed to 

 confer the appropriate title of the " velum." The endoplast in the examples 

 examined in the beginning of October by this same authority was found to form a 

 thick, knotted, or moniliform band, extending over three-quarters of a circle in close 

 vicinity to the truncated base. An apparent instance of the genetic union of a 

 larger and smaller zooid of the species after the manner of the Vorticellidae, and in the 

 accomplishment of which process the smaller unit presents the aspect of a mere bud- 

 like excrescence attached to the periphery of the larger one, has been reported by 



