GENUS PLAGIOTRICHA. 771 



observed ; a spheroidal eye-like corpuscle located in the median line near 

 the anterior extremity, and a similar one of slightly smaller dimensions 

 near the posterior extremity. Dimensions unrecorded. 

 HAB. Salt water : White Sea (Mereschkowsky). 



In general form this species is recognized by Mereschkowsky* as closely 

 approaching the Oxytricha (Amphisia) crassa of Claparede and Lachmann, while the 

 spheroidal anterior and posterior " eye-like corpuscles " find their equivalent in the 

 Actinotricha saltans of F. Cohn. In the absence of any other distinctly recognized 

 endoplast or nucleolar structure, it would seem highly probable, however, that these 

 so-called eye-like spots are in both cases modified homologues only of this last-named 

 element. Although not usual among the Hypotricha or other Ciliata, a similar 

 spheroidal endoplast, embodying a more densely granular central portion and a 

 hyaline peripheral border, obtains normally throughout the Flagellata. 



Holosticha Wrzesniowskii, Mereschk. sp. 



Body elongate-oval, rounded and slightly widest posteriorly, more 

 pointed and curved slightly towards the left anteriorly, a little over three 

 times as long as broad ; peristome-field narrow, rounded posteriorly, ex- 

 tending backwards almost to the centre of the body ; six large, subequal, 

 uncinate frontal styles ; two median rows of fine ventral, and two rows of 

 similar-sized marginal setae, the elements of the last-named series not 

 projecting beyond nor reaching the lateral periphery ; anal setae nine in 

 number, forming an even, slightly projecting posterior row; endoplasts 

 ovate, two in number ; contractile vesicle located close to the left lateral 

 border. Length 1-120". 



HAB. Salt-water : White Sea (Mereschkowsky). Motions sluggish. 



GENUS VIII. PLAGIOTRICHA, S. K. 



(Greek, plagios, oblique ; trichos, hair.) 



Animalcules free-swimming, ovate or elliptical, highly elastic ; peristome- 

 field narrow, arcuate, confined almost entirely to the left-hand antero-lateral 

 margin, and without any conspicuous reflected inner border ; the ventral 

 surface bearing eight or more frontal styles, one or more oblique rows of 

 ventral setae, a projecting fringe of marginal setae, and four or five anal 

 styles ; two or more slender caudal setae projecting from the posterior 

 extremity ; endoplasts two in number ; contractile vesicle single, spheroidal, 

 developed near the left-hand lateral border. 



This generic group is instituted for the reception of the Oxytricha strenua of 

 Engelmann, that species differing from all typical representatives of the genus 

 Oxytricha as here amended, in the characteristic oblique distribution of the ventral 

 setae which thus closely approaches that of Gastrostyla in the greater number of 

 frontal styles, and in the possession of hair-like caudal setae ; the peristome-field 

 likewise presents a well-marked modification. But for the absence of caudal setae, 

 the Oxytricha affinis of Stein might be also included in the same genus, and is here 

 temporarily associated with it. Sterki, indeed, as intimated further on, has already 



* "Protozoendes nordlichen Russland," 'Archiv fur Mikroskopische Anatomic,' Bd. xvi., 1878. 



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