IN THE ANIMAL KINGDOM. 79 



A sort of conjugation has been observed in some Infuso- 

 rians, and particularly in the allied order of Gregarinidse, 

 consisting mostly of parasites infesting the intestines of 

 insects ; but that attempts to assimilate it to the conjuga- 

 tion of the Protophyta are at least premature, is shown by 

 the diversity of the two processes in some important points. 

 For, firstly, the fusion which has been observed in Vorti- 

 cella and Gregarina by Stein and others, is not always con- 

 fined to a pair, but occasionally three have been seen to 

 Coalesce in this way ; and, secondly, the union does not 

 seem to be of the same nature, for after coalescing in this 

 manner, the animals have been seen to separate again in all 

 their integrity. Where it really is preliminary to the for- 

 mation of embryos, we may, therefore, more reasonably 

 consider it as a kind of intimate copulation, like that which 

 has just been described from Balbiani.* 



In connection with the reproduction of the Infusoria, two 

 other points seem to call for a short notice encystment, 

 and the transformations which have been described by some 

 authors. 



The encysting process has been most accurately observed 

 in Vorticella, but it probably occurs in all animals of the 

 class. A Vorticella about to become encysted contracts 

 slightly, closes the peristome or ciliated depression in which 

 the mouth is situated, and envelopes itself with a mucous 



* In some of the species observed by Balbiani, the union amounted to 

 an actual fusion of the individuals for more than two-thirds of their an- 

 terior part, and in all probability many supposed cases of incipient fission 

 have really been of this nature. Among the Entozoa, still more striking 

 cases of so-called conjugation have been observed. In Syngamus there 

 appears to occur a real fusion of tissue, and in Diporpa even a coalescence 

 of certain viscera between the two individuals, which, indeed, were first de- 

 scribed as one duplicated animal ; yet, in its bearing on reproduction, the 

 act seems nioi'e allied to ordinary copulation than to conjugation as it 

 occurs in the Protophyta, as both the individuals concerned have proper 

 generative organs of the ordinary type of the class. See Annals of Nat. 

 Hist., 2d Ser., VII., 428. 



