GENUS TRACHELOCERCA. 515 



remainder of the body, and which antero-lateral position of the mouth forms the 

 essential characteristic of the genus Pliialina. 



By Dujardin, and Claparfede and Lachmann, it has been considered desirable to 

 amalgamate the genus Trachelocerca with that of Lacrymaria, and to retain tlie last- 

 named title only, the single hitherto well-characterized member of the former genus 

 T. olor, being represented by them as differing too slightly from the ordinary 

 Lacrymaria. to claim independent generic recognition. It has been decided 

 here, however, to retain both of these two titles, numerous animalcules being 

 now known that form collectively two natural groups, between which it is easy 

 to discriminate when thus separated, but whose specific identification would be 

 attended wth much inconvenience were they collectively compared. In pursuance 

 of this decision, all those forms are retained in the genus Trachelocerca which agree 

 with T. olor in the possession of a specially elongate and highly extensile neck-like 

 anterior portion, in mostly having several irregularly distributed contractile vesicles, 

 and in the usually subterminal position of the anal aperture. In Lacrymaria, on 

 the other hand, as typified by the L. lagcriiila of Claparbde and Lachmann, there is 

 no specially elongate and elastic neck, the contractile vesicle is single and postero- 

 temiinal, and the anal aperture exactly terminal and immediately behind the con- 

 tractile vesicle. It is further a fact of note that all the short-necked specific forms 

 hitherto discovered, and here referred to the genus Lacrymaria, are strictly inhabi- 

 tants of salt water. While thus readily distinguishable in their adult conditions, a 

 developmental phase of Trachelocerca olor is presently sho\vn to correspond in a 

 remarkable manner with the typical adult condition of Lacrymaria lagemda. 



Trachelocerca olor, Miill. sp. Pl. XXVII. Figs. 29-31. 



Body subfusiform, usually attenuate posteriorly, the neck-like anterior 

 portion exceedingly elastic and contractile, often, in extension, equal to four 

 or five times the length of the body ; cuticular surface finely ciliate, obliquely 

 striate in two directions ; contractile vesicles two or three in number ; endo- 

 plast double, with a distinct endoplastulc. Length of extended body 

 1-140". Hab. — Pond water. 



This species was one of the earliest known infusorial forms, it having been 

 first figured and described by Baker in the year 1752 under the title of the " proteus," 

 while in Miiller's works it receives the three names of Vibrio proteus, V. olor, and 

 V. cygnus ; its relegation to the genus Trachelocerca was subsequently accomplislied by 

 Ehrenberg. The aspect of the animalcules of this species, as they swim gracefully 

 through the water, extending and contracting their attenuate and wonderfully exten- 

 sile necks, or thrusting them from side to side in search of food among the con- 

 fervoid filaments or vegetable debris which they usually affect, is, as implied by 

 its specific title, not unlike that of a swan, or is perhaps still more suggestive 

 of the restored figures of the long-necked mesozoic Plesiosauri, contained in 

 popular geological treatises. It has been frequently observed by the present 

 author that two individuals of this species are almost invariably found in close 

 proximity, and appear to be guided in all their movements by a certain com- 

 munity of action. The Trachelocerca viridis, T. linguifera, and T. biceps, and also 

 the Lacrymaria proteus of Ehrenberg, are regarded by Claparfede and Lachmann 

 as varieties only, or imperfectly observed examples, of this exceedingly protean 

 and variable species. In this manner the first-named is distinguished merely by 

 the presence of engulfed and incorporated chlorophyll-granules ; T. biceps would 

 be a monstrosity with a double neck, or a zooid undergoing longitudinal fission ; 

 while the variety with a rounded posterior extremity, described under the title 

 Lacrymaria proteus, probably represents an animalcule whose contour is abnomially 

 rounded and inflated by the ingestion of food-particles. The Trachelocerca linguifera 

 of Perty, said to differ from T olor'm the form of the oral region, which is described 

 as being surmounted by a movable flap or tongue-like process, practically corre- 



