744 ORDER HYPOTRICHA. 



effected by Wrzesniowski,* in company with the foregoing and two following species. 

 The observation of this animalcule by so many investigators sufficiently indicates its 

 plentiful and cosmopolitan distribution, it being indeed one of the most familiar of 

 its class, and, though not social in its habits, is rarely absent from pond water con- 

 taining the commoner species of duckweed, such as Lemna minor or trisuka. 



The author has recently, December 1878, met with examples of this species at 

 an earlier period of growth than has apparently been previously described, and an 

 attentive observation of these onwards to the assumption of their normal adult 

 form has yielded data of high interest closely parallel to those placed on record 

 at page 794 concerning the more typical Hypotrichous species Aspidisca costata. 

 This earlier condition of Litonotus fasciola, represented at PI. XLII. Fig. 8, was, 

 when first discovered, regarded as a strange and apparently undescribed in- 

 fusorial type. Its contour was remarkable, most closely resembling the husk or 

 palea of a barleycorn or some other cereal, the broader end representing the anterior, 

 and the pointed one the posterior extremity of the animalcule. The dorsal surface 

 was inflated, and with the exception of one long central and two proportionally 

 shorter lateral keel-like ridges, smooth and glabrous throughout. These ridges 

 jutted out slightly at the anterior margin, imparting to this region a dentated aspect. 

 A spherical contractile vesicle was conspicuous towards the posterior extremity, the 

 parenchyma in its immediate vicinity being slightly granular, though everywhere 

 else perfectly transparent ; no trace of an endoplast or nucleus could be detected 

 at this early period of its development. With the utmost difficulty, using a power 

 of 300 diameters, the flattened or somewhat concave ventral surface was discovered 

 to be clothed throughout with exceedingly fine, closely set, vibratile cilia, these cilia, 

 as time progressed, becoming longer and more distinctly visible. At the end of 

 about half an hour after commencing the observation of this animalcule, the first 

 indications of an impending metamorphosis were perceived. The body, which had 

 hitherto appeared to be enclosed by a rigid and, as already remarked, palea-like 

 dorsal shield, gradually assumed a flexible consistence, while the previously broader 

 and denticulate frontal border became rounded and contracted. The several linear 

 keel-like ridges on the dorsal surface likewise grew more obscure, and finally, with 

 the exception of a faint remaining trace towards the anterior extremity of the central 

 and longest ridge, entirely obliterated. A series of slightly larger pre-oral cilia was 

 now distinctly visible along the left-hand border of the anterior region, and also, 

 with careful manipulation of the light, the central double endoplast characteristic of 

 the adult representatives of the genus. At this stage of its growth, and after the 

 expiration of a little over one hour from the commencement of the author's investi- 

 gation, the animalcule presented the appearance indicated at PI. XLTI. Fig. 9 ; 

 the passage onwards to the fully matured specific form, involving little beyond the 

 greater prolongation, curvature towards the right, and increased flexibility of the 

 anterior or neck-like region, was completely accomplished within the succeeding 

 hour. It is worthy of remark that Litonotus fasciola, in its most abnormal and 

 earliest observed condition of development, as above described, resembles, to a 

 great extent, excepting for the absence of the pharyngeal armature, the adult form 

 of Scaphidiodon navicula, and more especially the shorter and broader varieties of 

 the species represented by O. F. Miiller at pi. xxvii. figs. 9-12 of his ' Animalcula 

 Infusoria,' under the title of Trichoda navicula. The so-called Drepanomonas dentata 

 of Fresenius * is apparently also identical with the immature condition of Litonotus 

 fasciola as just described^ 



Litonotus varsaviensis, Wrz. PL. XLII. FIG. 4. 



Body elongate, linear, transparent, flexible but scarcely contractile, five 

 or six times as long as broad, rounded posteriorly and not produced into a 

 distinct tail-like portion, tapering gradually towards the anterior extremity, 



* ' Zeitschrift fur Wissenschaftliche Zoologie,' Bd. xx., 1870. 



f ' Beitrage zur Kenntniss Mikroskopischer Organismen,' Taf. x. figs. 25-28. 



