GENUS OXYRRHIS. 427 



able retrogressive motions of the species in its more active state. No one, neverthe- 

 less, would dream, on similar grounds, of correlating with the tail end of a cuttle- 

 fish or lobster the functions of a cephalic region, simply because that extremity is 

 directed foremost during natation. 



In connection with the retrogressive motions of Oxyrrhis, it is worthy of remark 

 that it is the only free-swimming infusorial type, at present known, in which a flagellate 

 appendage serves, as in that of a spermatozoon or a Bacterium, the purpose of 

 propelling in place of drawing the body through the water. Professor E. Ray 

 Lankester (see Family ANISONEMID^E) has proposed to confer upon such an organ 

 of propulsion the distinctive title of a " pulsellum." 



Oxyrrhis marina, Duj. PL. XXIV. FIGS. 53-61. 



Body conical or helmet-shaped, subcylindrical, rounded posteriorly, the 

 anterior margin obliquely and unsymmetrically notched or emarginate, the 

 notch being produced further backwards on the left side, the superior angle 

 of the same region more or less conically prolonged ; flagella long and 

 slender, issuing from the posterior extremity of the oblique frontal emargi- 

 nation ; oral aperture elastic, capable of incepting food-particles of con- 

 siderable size ; endoplasm transparent, enclosing food-globules and vacuolar 

 spaces, its external surface smooth ; contractile vesicle anteriorly located. 



Length of body 1-900" to 1-500". HAB. Salt water. 



The or'ginal description of this species, as given by Dujardin* and herewith 

 reproduced in abstract, appears at first sight scarcely reconcilable with the type 

 indicated in the foregoing diagnosis. 



" Body colourless, subcylindrical, rounded posteriorly, the anterior border 

 emarginate, produced superiorly into a long, conical point, external surface 

 rugose ; flagella three or four in number, produced laterally from the bottom 

 of the anterior emargination. Length 1-500". HAB. Saltwater? 



The species, as above described, was obtained by Dujardin in salt water from the 

 Mediterranean containing Ulva, which had been kept standing fcjr many months. 

 The considerable number of flagellate appendages accredited to the type by its 

 discoverer, and as delineated in his original illustration of the type, reproduced at 

 PI. XXIV. Fig. 53, constitutes a feature of distinction which would appear to establish 

 the claim of the present form to a separate specific or even generic title. It is 

 evident, however, that Dujardin's presumed three or four flagella represent only the 

 optical aspect of the two appendages now shown to exist, when thrown into their 

 characteristic convolutions, as presently described. The irregular rugosity of the 

 external surface of the body, again attested to in Dujardin's diagnosis, and as 

 evidenced by his accompanying illustrations, coincides with the appearance merely 

 of the miscellaneous mass of food-material usually accumulated within it. A more 

 detailed account of the results of the author's investigation of this flagellate form, as 

 examined in abundance at St. Heliers, Jersey, both in water brought direct from 

 the sea and in long-standing hay infusions compounded with the same medium, may 

 now be proceeded with. 



It was not until examples had been killed with the aid of osmic acid and sub- 

 mitted to a magnification of 800 diameters, that the precise number and character 

 of the flagellate appendages, as here recorded, were accurately determined. Under 

 these auspices it was shown that these were two in number, similar in character, 



* ' Histoire des Zoophytes Infusoires,' Paris, 1841. 



