62 THE AMERICAN MONTHLY [April, 



protective sheath being equally as ready as its unprotected relative to fold 

 together its vibratile appendages and to leap backv^ard into the rearmost re- 

 gion of the lorica, whence it slowly extends itself when all danger is past, 

 and as slowly and cautiously expands the body and sets in motion the ciliary 

 circles. The type of the family is the common Vorticella, an infusorian so 

 well known, both in connection with its appearance and the nervous coiling 

 of its pedicle or foot-stalk, that no further reference to it is here needed. 



In addition to the separation of the members of the family into free-swim- 

 ming and sedentary form's, and the further division of the permanently at- 

 tached zooids into loricate and illoricate groups, the unprotected sedentary 

 animalcules are still further subdivided into two sections, according as they 

 are sessile or lifted upon a pedicle, while the pedicle may be either rigid or 

 contractile, simple or compound. Thus by a very natural method of classi- 

 fication the VorticellidcB are readily identified even bv the beginner, and he 

 is then prepared for further study of their structure. 



In Vorticella^ the typical genus of the family, there exists, immediately 

 beneath the cuticular surface, an extremely thin and delicate but highly con- 

 tractile layer surrounding the body as with a muscular sheet or investment, 

 and continued through the pedicle or foot-stalk as a stout and usually conspicu- 

 ous muscular thread, whose contractions are the cause of the very sudden 

 backward leaping of the animalcule wdien under observation. This muscu- 

 lar sheath of the body is extremely delicate, being apparent only under 

 strong amplification and after careful scrutiny. Its contractions, however, 

 are the cause of the body's unexpected assumption of the subglobular form, 

 which sometimes follows the coiling of the pedicle after a short but appreci- 

 able interval. The muscular thread of the pedicle in I'oi-ticella^ Carc/iesiu?)?., 

 and Zoothamniu77i is a long spiral within an external hyaline sheath, the 

 latter seeming to take no more active part in the muscular movements than 

 the human skin takes in the movements of the finger or other muscles. This 

 sheath appears to be elastic only, occasionally scarcely that, and to be con- 

 tinuous with the external cuticular coat of the body. The muscular thread 

 varies somewhat in character in the various species of l^orticella, often en- 

 closing small, granular particles, especially noticeable near the edges, while 

 in some species it exhibits larger crimson or bright green corpuscles. 



The pedicle of I'orticella is always unbranched, and normally bears but a 

 single body. When two Vorticellce are observed on the summit of the same 

 pedicle one is there temporarily only, being the result of longitudinal repro- 

 ductive fission. It will soon be seen to develop a posterior circle of cilia, 

 which, by their rapid vibration, speedily twist the body free, hurrying it 

 away to seek a pleasant spot for the erection of a pedicle and a repetition of 

 the act of fission. When \ orticella is in uncomfortable surroundings it will 

 often develop this posterior ciliary wreath and leave the pedicle to skurry 

 away for more congenial quarters. If w^atched it will be seen to skim over 

 many apparently pleasing surfaces, with the ciliated extremity downward, 

 and, having selected a favorable location, the secretion of a new pedicle is 

 begun, the posterior cilia are absorbed, the frontal region is expanded, and 

 the anterior cilia are again spread and put into vibration. This ability to twist 

 free from the foot-stalk at will is one of the characteristics of all the pedicel- 

 late Vorticellidfe. 



There are genera in the family whose pedicle, unlike that of Vorticella^ is 

 compound and dendroid, its branches spreading at the summit of the com- 

 mon trunk, while the living animalcules are stationed singly or in groups on 

 the ends. In some of these colonial Vorticellidae the entire tree-like pedicle 

 is rigid, the soft bodies alone contracting (^JEpistylis) ; in' others the main 

 stem, the branches, and the bodies all contract together {Zoothamnium) ; in 



