60 THE AMEBIC AN MONTHLY [April, 



both as single individuals and as those populous aquatic clouds which they 

 so often produce. In connection with this profusion, the writer has recently 

 seen the common Parajncechim aiirelia (one of the Holotricha) so profusely 

 developed in a vegetable infusion that they formed, next the side of the glass 

 vessel, a whitish mist fully one-tenth inch in depth, and extending one-third 

 the distance across the jar six inches in diameter, and for about the same 

 distance around it. 



The present paper deals, in an elementary way, with but one family group 

 in one of the above orders, the Vorticellidae in the Peritricha, none of which, 

 when matui'e, are free-swimming forms. At one stage of their life, how- 

 ever, they all, so far as known, pass through a migratory phase, settling 

 down sooner or later to become permanently sedentary at the selected point 

 of attachment. We shall here deal with the matui^e forms alone, further 

 limiting our attention to those whose habitat is in fresh water, or in animal 

 or vegetable infusions made with fresh water in contradistinction to salt. 

 The object of the paper is to call attention to the interesting forms of seden- 

 tary Peritricha so often met with by the amateur microscopist, especially in 

 early spring, and often passed by with a hasty glance, and a feeling of regret 

 that so little can be learned of them from the books within reach. The 

 mere learning of the name is a help towards further self-instruction, if the 

 learner cares to follow up the clue thus obtained. Space forbids an entrance 

 into the details of microscopic anatomy, or even into extensive description ; 

 only the most concise diagnoses of the genera can now be given. This par- 

 ticular family group has been selected on account of the grace and the inde- 

 scribable charm of its members, and by reason, as well, of their abundance 

 and the frequency with which the student of microscopical pond-life will 

 meet them. 



The Peritricha includes ciliated infusoria whose vibratile appendages are 

 borne on one or both extremities of the body ; but the family here referred to 

 includes only those whose ciliary circles are confined to the anterior region. 

 There may be a single ciliary wreath extending around the edge of the 

 frontal border, approaching in a more or less spiral course the somewhat 

 eccentric mouth ; the wreath may be more nearly circular, or it may be 

 supplemented by from two to six additional ciliary circles. The central 

 space bounded by the cilia may occupy the entire frontal surface of the body, 

 as in the common Vorticclla ; it may be a level or an oblique plane, or a 

 more or less strongly convex dome. In any case the region bounded by 

 these vibratile hairs is known by the very appropriate name of the ciliary 

 disc, an organ that is somewhat diverse in character and appearance. In 

 some genera this ciliary disc is not more lofty than the anterior body-margin ; 

 in others it is conspicuously elevated on a narrow, supporting neck, while 

 its frontal surface may be so strongly turned away from the central axis ot 

 the bod}' that it becomes one-sided. In other genera {Spiroc/iona and 

 Ope?'C7ilai'ia) it is accompanied bj^, or it even bears, a colorless transparent 

 membrane, in appearance like a hyaline collar, the object of which is to 

 assist in directing the food into the proper channel. 



The movements of the cilia are so rapid that they are visible only by their 

 effects, or only at those points where two circles seem to meet and pass each 

 other, the appearance then being that of a fine, motionless bristle, an optical 

 illusion sometimes leading the inexperienced observer to imagine that the 

 infusorian has its cilia represented by two setae. These energetic movements 

 subserve one purpose only — the collection of food particles from the swirling 

 eddies produced by their action, and the directing of those particles into the 

 waiting oral aperture, whence they enter through a distinctly developed 

 pharyngeal passage into the substance (endoplasm) of the body, accompanied 



