594 



SYSTEMATIC HISTOEY OF THE INFrSORIA. 



and from O. herherina (xxix. 4), whicli 

 it closely resembles in its general orga- 

 nization, by its length and width being 

 much nearer equal, and by its not being 

 bent backwards on the stem when con- 

 tracted. Stein describes its Acineta and 

 the ciliated embryo resulting from it. 

 The stem is subject to great varieties ; 

 but these all agree in the stem expanding 

 from its base in a more or less marked 

 manner, in the branches being all of equal 

 length, and, in consequence, the zooids 

 elevated at different heights. The stems 

 of the oldest generations are low, and 

 have but few animalcules upon them, 

 which are seated on short, cun'ed, and 

 enoi-mously thick branches, such as are 

 seen in no other OpercularicB. The 

 whole surface of the stem is covered with 

 numerous, closely-placed, shallow and 

 deep transverse folds or constrictions, 

 which give it a Imotty appearance ; it is 

 also longitudinally striated. In younger 

 generations the stems are more densely 

 branched ; but the branches are not ex- 

 traordinarily thickened, being as slender 

 as those of the larger groups of O. arti- 

 culata, and, like these, have only here and 

 there transverse markings, — for instance, 

 at the angles of the branches. They are 

 also longitudinally striped, and differ 

 fui'ther from O. herherina by their ex- 

 pansion upwards towards the base of 

 the superposed animalcule. On aquatic 

 Crustacea and Mollusca. 



O. stenostoma (Stein). — Body p}Ti- 

 fonn, widest in front of the middle line, 

 rounded anteriorly, with a very narrow 

 periston!, and behind the middle strongly 

 contracted, so as to assume the appear- 

 ance of a pedicle. The disc of the rotary 

 organ is very narrow across, fringed with 

 a single row of cilia; the membranous 

 process from the oral cavity rises only so 

 much above the periston! as to fori!i a 

 narrow ani!ular ridge. Ni!cleus long and 



Genus ZOOTHAMNIUM (XII. 67, 68, 69).— Comprehends Vorticellina 

 with a spirally flexible branched pedicle ha\ing an internal muscle. The 

 stalked corpuscles are of different shapes ; a wreath of cilia surrounds the 

 frontal region. The mouth simple and lateral. Numerous round stomach- 

 cells (vacuoles) can be demonstrated by artificial feedings. Self-division has 

 been observed. 



The more accm^ate examination of Stein supplies additional details, and 

 corrects those above, as given by Ehrenberg. The so-called frontal region is 

 the peristom of Stein, which presents a rounded tumid border, but no cilia ; 

 for these organs form a fringe around a ciliary disc within the circumference 

 of the peristom, which can be protruded beyond, or retracted withiii it. In 

 short, Zoothamnium, like other Vorticellina, has a '' rotary organ," which, by 

 the whirling of its cilia, di'aws inward to the mouth, situated on one side of 



horseshoe-shaped ; contractile space cir- 

 cular, placed near the coi!!i!!encement of 

 the oesophagus. Stem branched dichoto- 

 mously, but short, whei!ce the individual 

 animalcules (not more than 4-6 in num- 

 ber) are in near apposition. 1-900"; 

 length of stem 1-360". The stiff stem is 

 si!!all relatively to the body, striated 

 longitudinally, and obscurely wriulded 

 transversely. On aquatic Mollusca. 



O. 7mcrosto7na (Stein) (xxx. 37). — 

 Very similar to the last-named species, 

 like this, it forms a lowlj-branched stem 

 bearing few animalcules. The branches 

 are comparatively thin, and mostly 

 marked by thickly-set annular constric- 

 tions, rendering it more or less crooked 

 and knotty. Some sten!S, however, are 

 quite smooth, and also without trace of 

 longitudinal striae. The animals, when 

 extended, are pear-shaped, and have a 

 constriction behind the i!!iddle, and in 

 front a very narrow periston!. Rotary 

 organ with a shoi-t steii! and a narrow 

 disc; on the opposite side of the oral 

 cavity is a tongue-like i!!en!bran'Ous pro- 

 cess. " The oral cavity is comparatively 

 narrow; the digestive tube short, the 

 contractile vesicle lies near its upper 

 end, and the C!irved, hook-like nucleus 

 behind the rotary orgai!. In contraction 

 the anii!!al retains its pyrifor!!! figure, 

 and is thrown into annular folds poste- 

 riorly. "VVTien nrore strongly contracted, 

 it becomes oval. Greatest length 1-280" ; 

 width 1-450". On the feet of Crustacea. 



O. nutans (Stein) = Epistylis nutans 

 (Ehr.) ; but the description by Ehren- 

 berg requires to be niodified by the dis- 

 coveries of Stein, to render it correct and 

 characteristic. The t^^o-lipped mouth 

 is a misapprehension of the rotary organ 

 and membranous process of the oral 

 cavity, and the retractile palate is equi- 

 valent to the rotary organ of Stein. 



