554 ORDER HOLOTRICHA. 



through and displacing them as it advances. The accredited immature phases of this 

 animalcule, as represented by Figs. 8 to 15 of the accompanying plate, are remark- 

 able both for their dissimilarity in general from one another and from the parent 

 form, circumstances which, as fully recognized by their discoverer, render their 

 identification with Trichonympha — pending the actual tracing of their development 

 into the adult type — purely tentative. In the imbricated modification delineated at 

 PI. XXVIII. Figs. 9 and 11 more especially, it is worthy of note that a far closer 

 resemblance subsists between them and the phases of Pyrsoiietna vertens illustrated 

 by Figs. 19 and 20 of this plate, than between the same and the adult form of 

 Trichonympha. Respecting the zoological position and afiinities of the type now 

 under discussion. Professor Leidy declares himself to be in some doubt whether to 

 regard it as a Ciliate Infusorian, a Gregarine, or a Rhabdoccelous Turbellarian, the 

 evidence, however, to his mind, favouring its relegation to a position with the first or 

 midway between the first and second groups. Afiinities with the Gregarinida are, 

 in his opinion, indicated in connection with the separation of the adult body into 

 two distinct regions. A similar degree of differentiation is nevertheless manifested 

 in various ordinary Ciliate Infusoria. As illustrated by the generic types Lacrymaria, 

 Trachdocerca, Phialina, and Mcsoditiium, in all of which a separate head-like region 

 is distinctly recognizable. In all other respects Trichonympha conforms essentially 

 with the normal Holotrichous plan, the greater length and fineness of the ciliary 

 appendages being, seemingly, a more pronounced development of what commonly 

 obtains among the Opalinidae and other endoparasitic Infusoria, and in which a 

 matted or tufted character of the cilia is of frequent recurrence. It is at the same 

 time worthy of remark that the great length and apparently serial plan of disposi- 

 tion of the cilia in Trichonympha confer upon these organisms no inconsiderable 

 resemblance to the larvas of certain Chastopodous Annelids, such as A'crine, in 

 which fascicles of long fine setae are in a somewhat similar manner produced, 

 chiefly from the anterior region of the body. 



GExXUS II. PYRSONEMA, Leidy. 



Animalcules freely motile, more or less elongate, exceedingly flexible 

 and elastic, apparently finely ciliate throughout ; possessing in addition a 

 narrow, cord-like, undulating border which extends the whole length of the 

 body ; an oral aperture seemingly existing, but its position undetermined. 

 Endoparasitic within the intestine of white ants. 



Pyrsonema vertens, Leidy. Pl. XXVIII. Figs. 16-20. 



Body highly flexible and contractile, elongate-fusiform when extended, 

 clavate or pyriform in the contracted state ; while moving, exhibiting longi- 

 tudinally spiral and parallel lines, these at the extremities or at the ano^les of 

 flexure presenting the aspect of serrated projections, having a rapid wavino- 

 motion, resembling the movement of flames, and often communicatino- to 

 the body a screw-like aspect ; cilia when present short and of even length, 

 distributed throughout the entire surface of the body ; a narrow cord-like 

 prominence or membrane frequently extending the whole length of the 

 body, sometimes projecting at one extremity, moving in long, angular waves, 

 and flexing the body in accordance with its movements ; endoplasm finely 

 granular, enclosing a round or oval endoplast, which is located a little in 

 advance of the median line ; contractile vesicle not observed ; position of 



