GENUS ENCHELYODON. 503 



structure of a differential bounding wall or membrane, as also of its non-occupation 

 of a restricted position in the substance of the cortex. At the time of fullest 

 diastole a variable number of minute transparent lacunae filled witli water make 

 their appearance round the border of the contractile vesicle, communicating to it 

 a rosette-shaped contour, and remain as small independent vacuoles after the 

 contents of the central reservoir have been discharged, these then coalesce, and, 

 increasing in size, assume the same form and pursue a like course as the water 

 globule or vacuole just discharged. The food-matter, after the extraction of its 

 nutrient properties, is collected in the form of a globular pellet at the posterior 

 extremity of the body, and on its way towards and through the anal aperture 

 temporarily dislodges the contractile vesicle, forcing it to a considerable distance 

 forwards from its original position, but to which it again returns after the evacuation 

 of the excreta. 



Trachelophyllum pusillum, C. & L. 



Body elongate, flask-shaped, the anterior or neck-like portion very little 

 narrower than the remainder of the body, four and a half times as long as 

 broad ; contractile vesicle single, postero-terminal ; endoplasts two in number, 

 elongate-ovate. Length of body 1-625". Hab. — Stagnant water. 



Claparfede and Lachmann regard this form as probably identical with the 

 Trachelitis pusillus of Perty. 



Genus II. ENCHELYODON, C. & L. 



Animalcules free-swimming, elastic and changeable in form ; ovate or 

 pyriform, not produced anteriorly in a neck-like manner ; oral aperture 

 apical, followed by a well-developed membranous pharynx, the walls of 

 which are mostly longitudinally plicate ; anal aperture postero-terminal ; 

 cuticular surface finely and entirely ciliate throughout. Inhabiting salt and 

 fresh water. 



In constructing this genus upon the type next described, Clapar^de and 

 Lachmann left it in some doubt whether the walls of the conspicuous tubular 

 pharynx were simply membranous and longitudinally plicate, or whether they were 

 indurated or strengthened by a cylindrical fascicle of rod-like teeth, as in Nassula 

 and Prorodon. Assuming the balance of evidence to be in favour of the latter 

 of tliese two hypotheses, they placed it in close vicinity to Prorodon, and from 

 which, indeed, they represent it as differing chiefly in the greater elasticity 

 and finer ciliatiou of the cuticular investment, and in its slower movements. 

 Wrzesniowski, however, who has more recently made this type the object of a 

 special investigation,* has decided that the pharynx is membranous and longi- 

 tudinally plicate, as half-anticipated by Claparfede and Lachmann, this being demon- 

 strated by the circumstance that the tube with its plications becomes bent upon 

 itself, or in a sinuous manner, during the contractions of the animalcule. Accepting 

 Wrzesniowski's interpretation, the natural position of Eiichclyodoii is evidently close 

 to that of Trachdophylhim, from which it would, indeed, appear to differ only in the 

 absence of a differentiated and elastic neck-like portion. 



Enchelyodon farctus, C. & L. Pl. XXVI. Figs. 51-53. 



Body elastic, ovate and somewhat flattened, slightly narrowest anteriorly, 

 more than twice as long as broad ; pharyngeal passage long and narrow, 



* ' Archiv fiir Mikroskopische Anatomie,' Bd. v., 1869. 



