GENUS PARAM&CIUM. 487 



oral aperture situated at the posterior extremity of the buccal fossa, 

 followed by a distinct pharyngeal passage ; anal aperture postero-terminal ; 

 contractile vesicles two in number, spherical or stellate ; endoplast ovate, 

 with a laterally attached endoplastule ; trichocysts abundantly developed ; 

 endoplasmic and cortical layer in adult individuals usually coloured green 

 through the presence of enclosed chlorophyll-like granules. Length of 

 body 1-280". HAB. Marsh water. 



This animalcule is referred by Ehrenberg, in his great work ' Die Infusionsthiere,' 

 to the genus Loxodes ; Focke, in the 'Isis' for the year 1836, being the first to 

 distinguish it by the generic and specific titles that are here given. A highly 

 characteristic feature of this species, and one which attracted the notice of the earliest 

 investigators, is the powerful circulation of the endoplasmic constituents, constantly 

 and uniformly maintained within the interior of the animalcule's body. Associated 

 with the usual brilliant green hue of both the moving corpuscles and those of the 

 more firm and motionless cortical layer or exoplasm, this circulating phenomenon 

 imparts to the animalcule an aspect highly suggestive of the cyclosis or rotation of 

 the cell-contents of certain aquatic plants, such as Anacharis and Valisneria. A similar 

 circulation obtains, but is not so conspicuous, in the young and colourless individuals. 

 As shown by Stein's figures, and confirmed by the author's investigations, this 

 rotation of the body-contents exhibits a uniform motion, ascending on the left side 

 and descending on the right when viewed from a dorsal aspect, and may be thus 

 described as in conformity with the apparent motion of the sun or the hands of 

 -a watch when facing the observer. 



The reproductive phenomena of Paramacium, as manifested more especially 

 with the present species, have received a considerable amount of attention at the hands 

 of recent investigators. Balbiani's name is more especially worthy of notice in this 

 connection, he having been the first to demonstrate * that the previously so-called 

 process of multiplication by longitudinal fission of one animalcule was really the 

 more important act of conjugation or genetic union between two independent 

 zooids. In the accomplishment of this conjugative act two animalcules apply 

 themselves closely to one another by their oral or ventral surfaces, the parts thus 

 brought into immediate contact becoming intimately fused or united with each 

 other. In this closely united state the two animalcules may remain for a period of 

 five or six days or more, but ultimately separate and resume their previous inde- 

 dendent career. As the result of this conjugation the endoplast and endoplastule 

 undergo an important modification. Originally it was thought by Balbiani that 

 the last-named of these two structures was interchanged by the two united animal- 

 cules, and fulfilled the part of a male fecundatory capsule or testis with reference to 

 the endoplast, which remained stationary and was supposed to enact the role of a 

 female organ or ovary. As fully related, however, in vol. i. p. 94 et seq., more recent 

 investigation has not tended to confirm this hypothesis. At the same time it has been 

 demonstrated by Balbiani and numerous other later authorities that during or subse- 

 quent to this process of conjugation both the endoplast and endoplastule become 

 turgid and enlarged, the latter assumes usually a more or less striated aspect, while the 

 former breaks up into a variable number of spheroidal bodies, which become separated, 

 and are ultimately cast out of the body, and probably constitute reproductive germs 

 or ovules. In accordance with an earlier interpretation, it was assumed that the 

 endoplastule, in its striated condition, represented a bundle of spermatic elements. 

 The fact, however, that a similar striate aspect is frequently distinctive of this 

 structure during the more simple process of multiplication by transverse fission, as 

 also under like conditions of an ordinary cell-nucleus, has rendered this assumption 

 no longer tenable. The similarly manifested process of conjugation of Paramcecium 

 aurelia, as delineated by Ehrenberg, is reproduced at PL XXVI. Fig. 30. 



' Comptes Rendus, 1 1858. 



(03 ; * 



