GENUS VORTICELLA. 671 



frequently in association with an ordinary undivided 20oid that has become 

 liberated from its stalk ; or, as more rarely happens, the same zooid may enter upon 

 this condition of encystment without becoming separated from its pedicle. The sub- 

 sequent metamorphoses are in all cases identical. The animalcule contracts into 

 a subspheroidal form, and secretes around it a hyaline, chitine-like, ovate or sub- 

 spheroidal cyst, whose surface is frequently ornamentally facetted. The oral system, 

 contractile vesicle, and, with the exception of the nucleus or endoplast, all other 

 distinct features of the enclosed animalcule become next entirely obliterated. The 

 band-like endoplast, which previous to the process of encystment had already be- 

 come abnormally conspicuous, represents now the only essential differentiated 

 structure, and it is out of this that the sporular elements are evolved. Increasing in 

 dimensions at the expense of the surrounding protoplasm, it grows relatively larger, 

 much convoluted, or even branched. It next becomes constricted at regular 

 intervals, presenting a moniliform appearance, and finally separating at each con- 

 striction, the cyst is more or less completely filled with subspheroidal spore-like 

 fragments. Becoming matured, these sporular bodies are discharged, through rupture 

 of their capsule, as minute ovate or pyriform free-swimming animalcules, possessing 

 an anterior crown of cilia, which are likened by Everts to Trichodina (Halteria) 

 grandinella, but more correctly resemble the adult form of the genus Strombidium. 

 These free-swimming embryos multiply abundantly by transverse subdivision, incept 

 food by an oral aperture developed in close proximity to the anterior ciliary wreath, 

 and finally, becoming languid in their motions, attach themselves by their oral pole 

 to some submerged object. The pre-existing oral aperture and accompanying cilia 

 are now obliterated, new ones, as in an adult Vorticella, are developed at the opposite 

 extremity, and the attached portion, gradually lengthening, assumes the contour and 

 characters of the ordinary contractile pedicle. Illustrations of all the more charac- 

 teristic phases of this developmental process, as given by Everts, are reproduced 

 at PL XXXV. Figs. 33-46. 



An interesting example of the above reproductive form of encystment has been 

 recently recorded by Professor G. J. Allman,* in connection with a compound 

 Vorticellidan, apparently a species of Epistylis, obtained by him from a pond in 

 Brittany. Of this he states : " Among the ordinary zooids which are grouped in 

 spherical clusters on the extremities of the branches, there were usually some which 

 had become encysted in a very remarkable way, and without any previous conjuga- 

 tion having been noticed. These encysted forms were much larger than the others, 

 and had assumed a nearly spherical shape. The peristome and ciliary-disc had 

 become entirely withdrawn ; the contractile vesicle was still obvious, but had ceased 

 to manifest contractions ; brownish spherical corpuscles with granular contents, 

 probably the more or less altered chlorophyll-granules of the unencysted zooid (food- 

 material ?), were scattered through the parenchyma ; and the nucleus was not only 

 distinct, but had increased considerably in length. Round the whole a clear gelati- 

 nous envelope had become excreted. In a later stage there was formed between the 

 gelatinous envelope and the cortical layer of the body a strong, dark brown, apparently 

 chitinous case, the surface of which, in stages still further advanced, had become 

 ornamented by very regular hexagonal spaces with slightly elevated edges. In this 

 state the chitinous envelope was so opaque that no view could be obtained through 

 it of the included structures, and in order to arrive at any knowledge of these it was 

 necessary to rupture it. The nucleus thus liberated was found to have still further 

 increased in length, and to have become wound into a convoluted and complicated 

 knot. Along with the nucleus were expelled multitudes of very minute corpuscles, 

 with active Brownian movements. In a still later stage the nucleus had become 

 irregularly branched, and at the same time somewhat thicker and of a softer con- 

 sistence, while finally this element had broken up into spherical fragments, each 

 with an included corpuscle resembling a true cell-nucleus, the place of a nucleolus 

 being taken up by a cluster of minute granules." It is clearly evident that the form 



* Brit. Assoc. Reports, 1873, and President's Address to the Linnaean Society, 1875. 



