GENUS PODOPHR YA. 821 



Examples of this species were received by the author as recently as November 

 1 88 1, growing in tolerable abundance in company with Acineta mystacina and 

 A. lemnarum on Ranunculus and other water-weeds from the neighbourhood of 

 Dundee, remitted by Mr. John Hood. As first figured and described by Claparede 

 and Lachmann, the species of mollusc named in the foregoing diagnosis is cited as 

 the only habitat ; the fact, however, that this type is restricted to a much more 

 southern area suffices to indicate that the infusorian species is not strictly a com- 

 mensal of Paludina. As examined by the author, the tentacles of Podophrya elongata, 

 were found, in their contracted state, even under moderate enlargement, to be distinctly 

 annulate in a spiral direction, and on being submitted to the relatively high magnifica- 

 tion of six or eight hundred diameters presented the aspect given at PI. XLVIII. 

 Fig. 22, the spiral element being thus demonstrated to consist of a spiral crest or 

 ridge of granular consistence, developed externally to the shaft of the tentacle, its 

 convolutions becoming more widely separated or attenuate until vanishing with the 

 extension of the tentacle, and the more closely approximated and thickened in pro- 

 portion to its contraction. The function of this crest-like element is apparently 

 intimately connected with the contractile movements of the tentacle, being in this 

 manner analogous to the spirally disposed fibrilla of the stalk of a Vorticella^ 

 and also histologically and functionally homologous with the spiral granular ridges 

 developed on the external surface of the proboscis-like appendage of the genus 

 Ophryodendron. 



Podophrya mollis, S. K. PL. XLVL FIGS. 53-56. 



Body highly flexible, usually more or less triangular in outline when 

 expanded, sometimes ovate or pyriform, tapering posteriority, bearing two 

 antero-lateral fascicles of conspicuously capitate tentacles ; pedicle slender, 

 about twice the length of the body, straight, and even throughout ; con- 

 tractile vesicles one or two in number ; endoplast ovate. Length of body 

 i-iooo" to 1-240". HAB. Pond water, on various aquatic plants. 



Excepting for the entire absence of the separate investing pellicle or lorica this 

 type corresponds closely in contour and habits with Stein's " Acineta lemnarum" 

 originally regarded by that authority as a developmental condition only of Vorticella 

 nebulifera. The author has met with it abundantly on Lemna and other aquatic 

 plants, and on one occasion witnessed the process of transverse fission which as 

 manifested in this instance does not appear to have been previously recorded among 

 the representatives of this group. As a prelude to this process of fission two of the 

 tubular tentacles were extended to a great length, until finding a suitable fulcrum 

 for support they become firmly adherent to it ; within a short interval these two 

 tentacles coalesced, and becoming indurated, constituted as it were a second pedicle 

 joined on to the anterior extremity of the animalcule : the body of the zooid mean- 

 while grew more attenuate, and a considerable portion of the substance of its soft 

 plastic parenchyma passed over towards the newly formed pedicle. A constriction 

 now appeared in the centre of the body between the two attenuate extremities and 

 gradually deepened until a perfect separation was effected, the newly formed 

 product of this fission thus commencing its independent existence with an attached 

 pedicle and organization as complete as the zooid of which it but a short while 

 previously formed merely a constituent part. At PI. XLVI. Figs. 55 and 56 repre- 

 sentations of drawings made during the progress of this fissive process are herewith 

 reproduced. The stage represented by Fig. 56, if unaccompanied by the expla- 

 nation here given might be easily interpreted for an act of conjugation. This 

 species of Podophrya is remarkable among the other representatives of the same genus 

 for its great elasticity, the body assuming various attitudes on its stem and under- 

 going considerable modifications in external contour. When abandoning its more 

 normal triangular-shape for an ovate or pear-shaped outline it presents a close 



