376 ORDER FLAGELLATA-EUSTOMATA. 



has been demonstrated by the present author to be a transitional condition only of a 

 Radiolarian closely allied to, if not identical with, Acti7iophrys sol (see p. 225). 

 Stein, for reasons as yet unexplained, figures in his recently published volume,* as 

 members of the genus Astasia, biflagellate animalcules corresponding most nearly 

 with the forms upon which Dujardin has conferred the name of Hcteroncma, while 

 the typical representative of the present genus, the Astasia ( T?-achdit(s) trichophora 

 of Ehrenberg, is referred to Dujardin's genus Peranema, which, as just shown, 

 possesses no sound claim for retention. 



Astasia trichophora, Ehr. sp. Pl. XX. Figs. 17-21. 



Body highly metabolic, variable in shape, more usually irregularly 

 pyriform or clavate, widest posteriorly and tapering gradually towards the 

 pointed anterior extremity, the posterior end sometimes with a short caudi- 

 form prolongation ; flagellum thick and cord-like, about one and a half times 

 longer than the body ; contractile vesicle situated anteriorly, closely 

 adjacent to the centre of the pharyngeal track ; endoplast spherical, central, 

 of large size; endoplasm clear and transparent. Length of body I-I200" 

 to 1-370". Hab. — Marsh and stagnant water. 



This animalcule was first described under the title of Trachelius trichopJwrus by 

 Ehrenberg, who mistook the thick cord-like flagellum for an attenuate neck-like 

 prolongation of the body, similar to that met with in the ciliated genera Lacrymaria, 

 Amphihptus, and Trachelius. Claparede was the first to indicate its rightful position, 

 but not before it had been redescribed by Dujardin under the titles of \)Q\h Peranema 

 protrada and Astasia limpida. The varieties of contour assumed by this form are 

 indeed so manifold and protean, that it seems highly probable that many, if not the 

 majority, of species hitherto referred to the genus are merely slightly modified 

 expressions of this single type. In its movements, which are of two kinds, repent 

 and natatory, the body is at one moment perfectly symmetrical and perhaps almost 

 cylindrical, while during the next it is writhing in amoeba-like contortions, and, 

 compared with its former aspect, almost unrecognizable. These contortions, as 

 already remarked by H. James-Clark, do not consist, as in Amoeba, of an actual 

 outflowing of the substance of the sarcode or parenchyma, but from an exceedingly 

 variable puckering of the cuticular surface, always accompanied by a more or less 

 longitudinal contraction of the body. This is most clearly apparent when the 

 animalcule becomes doubled on itself by an abrupt retrogressive motion. 



Professor Clark f has proposed to demonstrate that the occasionally conspicuous 

 caudiform prolongation of the posterior extremity of the body of this species is the 

 rudimentary homologue of the trailing flagellum, or, as he has termed it, the "guber- 

 naculum" oi Anisonema and other biflagellate types. Its thoroughly inconstant and 

 fugacious character, however, scarcely favours this interpretation. Although the 

 possession by the representatives of the genus Astasia of a distinct terminal oral 

 aperture has been recognized since the time of Ehrenberg, the connection with this 

 structure of a distinct indurated pharynx or so-called buccal tube was first recognized 

 and described by Mr. H. J. Carter in his notes on the Infusoria of Bombay, pub- 

 lished in the ' Annals of Natural History ' for August-September 1856, his observations 

 in this direction being abundantly confirmed by the later investigations of Stein and 

 Biitschli. Mr. Carter, in the publication just referred to, has adopted for this species 

 Dujardin's name oi Astasia limpida. An illustration of the extreme elasticity pos- 

 sessed by the oral aperture of this type is furnished by one of Biitschli's figures, in 

 which an animalcule is represented as incepting a spherical organism, apparently a 

 monad, whose diameter considerably exceeds that of its own body. A corresponding 

 extensibility of the oral aperture is encountered in the biflagellate type Dinovwnas, 



'Infusionslhiere,' Abth, iii., 1878. t 'Mem. Bost. Soc. Nat. Hist.,' i\ 



