ENCYSTMENT. 63 



corresponding type of form with certain modifications, the areas between 

 the longitudinal ridges being transversely striate or otherwise ornamented, 

 is common to the encystments of various Vorticellidae, while a somewhat 

 similar one, having the elevated crests transversely placed, recurs in the 

 Acinete type Podophrya fixa. In many species, such as Stylonychia pustu- 

 lata and Pleurotricha lanceolata, the exterior surface of the spheroidal cyst 

 is closely studded with more or less irregular papilliform elevations. In 

 all these instances of simple or protective encystment, the animalcule upon 

 the return of favourable conditions assumes once more its normal aspect, 

 and, breaking through the walls of its temporary prison-house, resumes 

 its customary active habits. It is undoubtedly to the possession of this 

 simple self-protective faculty that the extensive distribution and prolonged 

 vitality of many infusorial forms is mainly due. Where the ponds, ditches, 

 or other tracts of fluid containing such animalcules become entirely dried up, 

 these latter run no risk of extermination. Throwing out around them their 

 transparent envelopes, they remain in a quiescent or torpid state until the 

 reappearance of the previous congenial surroundings, or, taken up by the 

 passing breeze, are wafted away in the form of dust until conditions are 

 encountered corresponding sufficiently with those under which they origi- 

 nally flourished. 



The encystment of the second order to be mentioned is of comparatively 

 rare occurrence, and, instead of being associated with a simple conservative 

 function, is an accompaniment of, or rather the prelude to, the phenomenon 

 of multiplication by binary division, and may for this reason be most 

 appropriately denominated " duplicative encystment." The preliminary 

 manifestations and aspect of the constructed cyst correspond essentially 

 with those recorded of the simply protective form ; but the animalcule 

 enclosed within its capsule, instead of resolving itself into a quiescent and 

 inert mass, divides itself by the ordinary mode of increase by transverse 

 fission, the two halves shortly after making their exit through the walls 

 of the cyst, smaller in size, but in all other respects corresponding struc- 

 turally with the single pre-existing zooid. Encystment of this special 

 type, in conjunction with other noteworthy data, has been observed by 

 Claparede and Lachmann of the Holotrichous form Amphileptus meleagris. 

 As recorded in detail later on, this animalcule is essentially predatory in 

 its habits, and is addicted to preying upon the stationary and defenceless 

 zooids of the Vorticellidan genus Epistylis, in the same manner that the 

 Myxopod Vampyrella feeds upon the frustules of the Diatom Gomphonema. 

 In a like manner also, having gorged itself to satiety, the devouring 

 A mphilepttis builds its cyst on the apex of the supporting stem of its latest 

 victim, and there undergoes the metamorphosis above described. Duplica- 

 tive encystment is recorded by Stein of Glaucoma scintillans, and in accord- 

 ance with the observations of that authority occurs also in Colpoda cucullulus, 

 in combination with that variety of the process next described. 



The third, and remaining form of encystment to be enumerated, closely 



