MICROSCOPIC FORMS OF ANIMAL LIFE. 



47 



FIG. 307. 



undergo an * encysting process ' corresponding with that of the Vorticel- 

 lina. 



441. Many, perhaps all, ciliated Infusoria at certain times undergo 

 an encysting process, resembling the passage of Protophytes into the 

 ' still' condition ( 231), and apparently serving, like it, as a provision 

 for their preservation under circumstances which do not permit the con- 

 tinuance of their ordinary vital activity. Previously to the formation of 

 the cyst, the movements of the animalcule diminish in vigor, and grad- 

 ually cease altogether ; its form becomes more rounded ; its oral aper- 

 ture closes; and its cilia or other 

 filamentous prolongations are 

 either lost or retracted, as is well 

 seen in Vorticella (Fig. 307, A). 

 A new wreath of cilia, however, 

 is developed near the base, and 

 in this condition the animal de- 

 taches itself from its stem, and 

 swims freely for a short time, 

 soon passing, however, into the 

 ' still' condition. The surface 

 of the body then exudes a gela- 

 tinous excretion that hardens 

 around it so as to form a com- 

 plete coffin-like case, within 

 which little of the original struc- 

 ture of the animal can be dis- 

 tinguished. Even after the COm- Encysting process in Vorticella microstoma : A, 

 i 9 -e xi, i, full-grown individual in its encysted state ; a, retrac- 



pletlOn 01 the Cyst, however, ted oval circlet of cilia ; 6, nucleus; c, contractile vesi- 

 thp rrmtaiTiprl anirnnlrnlA rnavcl 6 ; B ? a cyst separated from its stalk; c, the same 



Qa y m ore advanced, the nucleus broken-up into spore- 



Olten be Observed to move free- like globules; D. the same more developed, the origi- 

 Iv tvifliin if 1 ma\r anma nal body of the Vorticella, d, having become saccu- 

 JV Wltnm It, ana may Some- lated< a d containing many clear spaces;-at B, one 

 times be Caused to COme forth of the sacculations having burst through the envelop- 



from its prison by the mere appli- Sffifc di e hr mass> '' <mM " la ' the en " 

 cation of warmth and moisture. 



In the simplest form of the ' encysting process,' indeed, the animalcule 

 seems to remain altogether quiescent through the whole period of its 

 torpidity; so that, however long may be the duration of its imprison- 

 ment, it emerges without any essential change in its form or condition. 

 But in other cases, this process seems to be subservient either to multi- 

 plication or to metamorphosis. For in Vorticella, the substance of the 

 encysted body (B) appears to break up (c, D) into eight or nine segments, 

 which, when set free by the bursting of the cyst, come forth as sponta- 

 neously moving spherules. Each of these soon increases in size, develops 

 a ciliary wreath within which a mouth makes its appearance, and grad- 

 ually assumes the form of the TricJiodina grandinella of Ehrenberg. It 

 then develops a posterior wreath of cilia, and multiplies by transverse 

 fission; each half fixes itself by the end on which the mouth is situated, 

 a short stem becomes developed, and the cilia-wreath disappears. A new 

 mouth and cilia- wreath then form at the free extremity; and the growth 

 of the stem completes the development into the true Vorticellan form. 1 

 In Trichoda lynceus, again, the 'encysting process' appears subservient 

 to a like kind of metamorphosis; the form which emerges from the cyst 



1 Everts, 

 loc. cit. 



Untersuchungen an Vorticella nebulifera," quoted by Prof. Allman, 



