430 ORDER FLAGELLATA-EUSTOMATA. 



normally sedentary collared monads Codosiga, Salpingceca^ &c., have likewise been 

 observed by the author to exhibit retrogressive natatory movements, a circumstance 

 which might indeed be consistently predicated in connection with the motion of the 

 flaeellum and the direction of the current it engenders, as described at length at 

 P- 327. 



Genus I. HETERONEMA, Dujardin. 



Animalcules free-swimming, ovate or elongate, highly elastic and 

 metabolic ; flagella two in number, produced from the anterior extremity, 

 the one vibratile, the other trailing and adherent ; oral aperture distinct, 

 situated close to the base of the flagella, usually followed by a well-defined 

 pharyngeal tract ; endoplasm transparent, granular. Inhabiting salt and 

 fresh water. 



As originally instituted by Dujardin, the genus Heteroncma included but one 

 imperfectly defined specific type, H. marina, which has been usually regarded as 

 exhibiting too close a resemblance to Anisonema or Heteromita to merit independent 

 recognition. Two other well-defined specific forms are added to this genus by 

 Stein in his recently published volume which, while conforming with Dujardin's 

 original definition, manifest their distinctness from Anisonana, Hdcromita, and other 

 superficially corresponding genera in their extreme mutability of form, or in other 

 words highly metabolic character. 



Heteronema acus, Ehr. sp. Pl. XXIV. Figs. 14 and 15. 



Body in extension attenuate fusiform, widest a little behind the centre, 

 tapering towards and sharply pointed at each extremity, eight or ten times 

 as lono- as broad ; flagella slender, unequal, the anterior one, or tractellum, 

 extended rigidly in advance, equalling the body in length, the trailing 

 one, or gubernaculum, about half that length ; contractile vesicle situated 

 close to the anterior extremity ; a large, oval, endoplast-like structure in the 

 centre of the widest portion of the body ; endoplasm finely granulate. 

 Length of body 1-600" to 1-300". 



Hab. — Fresh water : Europe and Bombay. 



The form as defined in the foregoing diagnosis and accompanying illustra- 

 tions, is identified by Stein with the Astasia acus of Ehrenberg, and referred 

 to its present rightful position. An animalcule presenting a precisely similar 

 external contour and metabolic properties, is likewise figured as " an Astasia 

 with two filaments " in one of the note-books kindly placed at the author's disposal 

 by Mr. H. J. Carter, such animalcule having been encountered by that authority at 

 Bombay in the year 1856. In one of the delineations made hy Mr. Carter its 

 body is so contracted upon itself that the diameter considerably exceeds the 

 total length, the two anterior and posterior extremities projecting as mere points 

 from the flattened and almost discoidal central region of the body. A similar 

 turbinate or rotulate shape is commonly exhibited among the multitude of protean 

 configurations presented by Euglaia and Astasia, or by the isomorphic Cilio- 

 Flagellate genus Heteromastix. 



Heteronema globuliferum, Ehr. sp. Pl. XXIV. Figs. 16 and 17. 



Body highly metabolic and changeable in shape, mostly elongate-ovate 

 or pyriform when extended, with a truncate or rounded posterior, and a 

 narrower pointed anterior extremity, two or three times as long as broad ; 



