392 ORDER FLAGELLATA-EUSTOMATA. 



Raphidomonas semen, Ehr. sp. Pl. XX. Figs. 60-62. 



Body elongate-ovate, flexible and somewhat variable in form, usually- 

 rounded and widest anteriorly, tapering and slightly attenuate posteriorly, 

 from two and a half to three times as long as broad ; flagellum scarcely 

 equalling the body in length, issuing from the anterior oral fossa ; pharyngeal 

 chamber subtriangular or lunate, transversely placed ; contractile vesicle 

 single, anteriorly situated ; endoplast large, ovate, subcentral ; endoplasm 

 green ; trichocysts most abundant along the anterior margin. Length 1-575" 

 to 1-400". 



Hab. — Marsh water, among decaying Sphagnum ; movements sluggish, 

 vacillating. 



As originally described by Ehrenberg under the title of Monas (?) semen, this 

 species is distinguished by the presence of a peculiar triquetrous structure beneath 

 the frontal border, by the enclosure within its substance of numerous minute spicular 

 bodies, and by its apparent possession of fine vibratile ciUa. As now shown by 

 Stein * the first-named structure represents a capacious subtriangular pharyngeal 

 excavation, which communicates with the oral aperture and is homologous with the 

 still more conspicuous spheroidal one possessed by Cc^lomonas grandis ; the pre- 

 sumed cilia he has further demonstrated to coincide Avith the anteriorly placed tricho- 

 cysts in their exserted state, as shown at PI. XX. Fig. 61. In their more normal 

 retracted condition these trichocysts — coinciding with Ehrenberg's spicular bodies — 

 present the aspect of simple minute bacillar bodies which underlie, as an even and 

 closely set row, the entire frontal border, and are found distributed irregularly and 

 in various degrees of abundance throughout the remaining body area. Although 

 not taking the form of evenly distributed lines in the last-named region, they appear 

 from Stein's figures to maintain mostly a uniform longitudinal disposition. Meresch- 

 kowski's genus Merotricha, see p. 249, would appear to represent the only other 

 Flagellate animalcule to Avhich the existence of trichocysts has been accurately 

 demonstrated, though, in accordance with the recent investigations of O. Blitschli, 

 there is reason for believing that analogous structures are possessed also by 

 Chilomonas Paramecium. In neither instance, however, have they been shown to 

 possess a distinct capacity of extension and retraction, as is recorded by Stein of 

 Raphidomonas. 



Genus VII. CCELOMONAS, Stein. 



Animalcules free-swimming, monoflagellate, highly contractile and vari- 

 able in form, having a distinct anterior oral aperture, which conducts to a 

 capacious subspheroidal pharyngeal chamber ; endoplast and contractile 

 vesicle conspicuous, no trichocysts. Inhabiting fresh water. 



This genus is founded by Stein f on the Monas grandis of Ehrenberg, its dis- 

 tinctive feature being the capacious phaiyngeal chamber, usually filled with a fluid 

 substance, that follows upon the well-developed oral cleft. While a somewhat 

 similar pharyngeal excavation is developed in both Raphidomonas and Microglcna, 

 it does not in either of these latter types attain the proportions characteristic 

 of the present genus. More correctly, perhaps, this so-called " body-cavity," or 

 " Leibeshohle" as it is designated by Stein in his index to the various figures given, 

 may be compared with the vestibular fossa of VorticcIIa and other Peritricha, the 

 resemblance in contour between these structures being more particularly pro- 

 minent in the type previously described under the title of Raphidomonas semen. 



Infusionsthiere,' Abth. iii., 1878. f Ibid. 



