T. W. Engelmann on this Infusoria. 249 



seen to break up into several segments, of which two retain the 

 nuclear character, whilst the rest become perfectly homogeneous 

 and exhibit no nuclei in their interior. In other examples a few 

 nuclear-looking structures take their rise within the substance 

 of the nucleus, at the enlarged end of the elongated and some- 

 times ramified nucleus. According to Engeluiann's observations, 

 the germinal corpuscle arises by a constriction of a portion of 

 the enlarged nucleus, which proceeds to complete separation, 

 and contains within itself a nuclear particle ; for he has never 

 been able to discover such a body lying within a special cavity 

 of the nucleus. Moreover those spherical corpuscles which 

 differ from germinal bodies only by the absence of nuclei within 

 them, and which appear to originate by repeated fission of the 

 original nucleus, eventually become germinal and embryonic 

 corpuscles. Lastly, these embryonic bodies undergo repeated 

 fission, and are ultimately transformed into embryos. 



A very remarkable phenomenon was noted by Engelmann in 

 very many specimens of Stylonychia Mytilus containing embryonic 

 corpuscles, viz. that, in addition to these bodies, there were also 

 present in them several (often as many as four) examples of the 

 beautiful cysts of Podophrya fixa, which have been described by 

 Weisse under the name of Orcula. Among other specimens of 

 the same animalcule the same observer also met with some which, 

 instead of two nuclei, possessed two large clear spherical bodies. 

 In one of these animals, each globule presented a nucleus with 

 an irregular outline, giving off from its periphery several delicate 

 processes like those of Amoeba and other Rhizopods. Three 

 hours later, these nuclei had acquired a clustered outline, and 

 had evidently broken up into a multitude of sharply defined, 

 rounded particles, still retained in relation with the periphery of 

 the enclosing corpuscle by fine filiform processes. Seven hours 

 afterwards this specimen was unfortunately destroyed by the 

 evaporation of the water around it. 



In some other Oxytrichina, Engelmann finds similar condi- 

 tions of conjugation as in the Stylonychia quoted, and among 

 others in Pleurotricha lanceolate. Another phenomenon noticed 

 by him in the animalcule just named is that of encysting. The 

 resulting cysts are precisely like those of Stylonychia Mytilus in 

 appearance, but of much greater size. Conjugation was also 

 investigated by him in Oxytricha pellionella, in O. ferruginea, 

 and in O. parallela — the last-named a new species. 



To sum up the foregoing observations : — Two forms of con- 

 jugation occur in the class of Infusoria, but only one of these 

 appears to be connected with the process of reproduction. The 

 first form consists in the complete coalescence of two previously 

 distinct individuals into one being. Though hitherto noticed 



