344 OEyERAL HISTORY OF THE INFUSORIA. 



tributed over the surface of the animal, and a close row of much stronger ones 

 along a fold recalling the characteristics of StylonijcMa or of Oxytricha, 

 although the animal still wanted the general confonnation of the body 

 peculiar to either of these genera (XXIX. 23). All this time the darker 

 nuclear body or bodies had retained their existence and position, whilst the 

 contractile vesicle, on the other hand, grew smaller, apparently by the ex- 

 pulsion of part of its fluid contents to occupy the space left between the 

 animal and its capsule by the contraction of the former. The enclosed body, 

 when freed from the wall of the cyst, commenced moving, not in a regular 

 rotation, but in a jerking manner, from side to side as it tiu'ned, until at 

 length it ruptured the walls of its piison and made its escape. The animal 

 thus set at large presented the characters of Oxytricha (XXIX. 24) di- 

 stinctly enough to recognize it as belonging to the genus ; and at the same 

 time the numerous escaping germs and the rapid appearance of a multitude 

 of O.vytricha Pellionella of all sizes confirmed this view of their nature. 

 Nevertheless a slight difference existed between the newly- emerged indi- 

 viduals and mature specimens, — the former being more oval, and theii' contents 

 less hyaline, more granular, and of a yellowish colour by transmitted light : 

 still, specimens occurred of every intermediate shade. 



This observation by Auerbach demonstrates to us how completely modified 

 and actually lost the characters of an animalcule may be when it becomes 

 encysted even temporarily, during what has been termed the winter-sleep ; 

 for, as that writer shows, the O.vytricha-cjsts he discovered could not have 

 been ova, or a mere transitional phase to a higher form of existence. Similar 

 instances of cyst -evolution are recorded by other observers ; but generally the 

 whole histoiy of the cyst is not given, but only that portion in which an 

 actual animalcular form, in movement by means of cilia, has revealed itself; 

 such is the instance of AmphUeptiis Fasciola mentioned by Cohn (Zeitschr. v. 

 1854, p. 434). Furthermore, vaiiations in the internal appearance and per- 

 ceptible contents of cysts vary in different species, just as do theii' walls ; 

 thus, for example, in Odyfyicha-cjats the contractile vesicle had vanished and 

 appeared de novo only when its vital activity was resumed, — while in other 

 cases this sac or space never disappears, but is even more prominent than 

 the nucleus before the action of reagents, which is tnie of most, or of all, 

 Vorticellina. 



The particulars recounted by Mr. Brightwell respecting ZootJiamnimn 

 Arbuscida (' Fauna Infusoria of Norfolk,' 1848), which he thought indicative 

 of a mode of development by alternate generation, appear to us to represent 

 probably the act of encysting, or that degree of it assumed by gemmae prior 

 to detachment from their parent stem, and retained by them until they have 

 taken up a fixed position and proceed to develop a peduncle (see section 

 on Fission and Gemmation). We extract Mr. BrightweU's account, so that 

 our readers may form their own opinion of the nature of the phenomena 

 detailed : — ■ 



" Sept. 16th, 1846. Early in the morning of this day, we observed one of 

 the Zoothamnmm arbuscida, a large old specimen, w^hich had lost all its 

 small bell-shaped animals, but had several medlar-shaped buds or ova re- 

 maining upon it. It was seen to detach from its stalks nearly all these ova, 

 which went off as free animals. One of them soon after settled at the side of 

 the water-trough, and after agitating its anterior cilia it suddenly, and with 

 a kind of violent effort, opened into a cup-shaped form, and darted about 

 with great rapidity, occasionally settling, and darting off again. 



'* At nine in the morning, one of these buds, or ova, was observed fixed to 

 the glass by a sheathed pedicle ; a ciliary motion became perceptible at the 



