98 MANUAL OF ZOOLOGY. 



ovules after their liberation from the body of the parent are 

 developed into adult Paramceria. 



Other observers, however, are disposed to believe that this 

 " conjugation " of two Paramceda is not a genuine sexual pro- 

 cess, that the " nucleolus " is not a true testis, and that the 

 rounded bodies into which the " nucleus " breaks up can be 

 developed into new individuals directly and without contact 

 with a second reproductive element. 



Vorticella (fig. 33, C) is a beautiful flower-like Infusorian which is com- 

 monly found in fresh water, adhering to the stems of aquatic plants. It 

 consists of a bell-shaped body or "calyx," supported upon the extremity 

 of a slender contractile stem or "pedicle." The other extremity of the 

 pedicle is fixed to some foreign body, and its power of contraction is due 

 to the presence in its interior of a spiral contractile fibre, which is some- 

 times called the "stem-muscle." The edge of the bell or calyx is sur- 

 rounded by a projecting rim or border, called the " peristome, " within 

 which is a circular surface, the "disc," forming the upper extremity of 

 the so-called "rotatory organ." The disc is surrounded by a fringe of 

 vibratile cilia, forming a spiral line which is prolonged into the commence- 

 ment of the digestive canal. Near the edge of the disc is situated the 

 mouth, which conducts by its entrance or ' ' vestibulum " into a fusiform 

 canal or ' ' pharynx, " which terminates abruptly in the abdominal cavity. 

 The particles of food are taken in at the mouth, descend through the short 

 alimentary canal, and enter the abdominal cavity, where they are subjected 

 to the general rotation of the " chyme-mass," being finally excreted by an 

 anal aperture which is situated near the mouth and within the vestibule. 

 As in Paramcecium, the body in Vorticella is composed of an outer ' ' cuti- 

 cle," a central "chyme-mass," and an intermediate "cortical layer," 

 which contains a contractile vesicle and a band-like nucleus. 



Reproduction in Vorticella may take place by fission, or by gemmation, 

 or by a process of encystation and endogenous division. In the first of 

 these modes the calyx becomes indented in a longitudinal direction viz. , 

 from the pedicle to the disc ; and the groove thus formed becomes gradu- 

 ally deeper until the calyx is finally divided into two halves supported 

 upon the same pedicle. On one of these cups a "posterior" circlet of 

 cilia is then formed in addition to the "anterior" circlet already existing 

 (i.e., a fringe of cilia is developed round that end of the calyx which is 

 nearest the attachment of the pedicle and furthest from the disc). The 

 cup (fig. 33, D), thus furnished with a circlet of cilia at both extremities, is 

 then detached, and swims about freely. Finally, the anterior circlet of 

 cilia disappears, and this end of the calyx puts forth a pedicle and becomes 

 attached to some foreign object. A new mouth is now formed within what 

 was before the posterior circlet of cilia ; so that the position and function 

 of the two extremities of the calyx are thus reversed. 



In the second mode of reproduction namely, that by gemmation 

 exactly the same phenomena take place, with this single difference, that 

 in this case the new individual is not produced by a splitting into two of 

 the adult calyx, but by means of a bud thrown out from near its proximal 

 extremity. This bud is composed of a prolongation of the cuticular and 

 cortical layers of the adult with a caecal diverticulum of the abdominal 

 cavity or chyme-mass. It soon develops a posterior circlet of cilia, the 

 connection with the parent is rapidly constricted until complete separation 

 is effected, and then the process differs in no respect from that described 



