250 T. W. Engelmann on the Infusoria. 



only in some of the Oxytrichina, its occurrence is rendered pro- 

 bable, by Claparede's researches, in Vorticetta microstoma, Car- 

 chesium polypinum, Epistylis brevipes, and in several Acinetina. 

 All that can be predicated with certainty respecting this variety 

 of conjugation is, that it has no direct relation to the process of 

 reproduction, but appears analogous to the coalescence observed 

 between individuals of the class of Rhizopods, particularly those 

 of the genus Actinophrys. 



The second form of conjugation proceeds by means of a union 

 of a portion of the bodies only of two individuals, as a rule, of 

 their anterior parts, in the region of the mouth ; it persists 

 several days, and then the animalcules once more separate. 

 When separation has occurred, the two beings are found changed 

 in various ways, both externally and internally, from their ori- 

 ginal characters, although, after the lapse of some days more, 

 those primitive features are resumed. This statement holds 

 good, at least, with respect to the Oxytrichina and Euplotina. 

 But in the case of the Paramecia and Colpidia, and other holo- 

 trichous Infusoria, whose organization differs widely from that 

 of the other two families named, the recently conjugated indi- 

 viduals differ very little or scarcely in any perceptible degree in 

 external characters from the normal form. The purpose served 

 by this second mode of conjugation, as particularly illustrated in 

 the Paramecia, stands in immediate relation with the process of 

 sexual reproduction. Another conclusion arrived at from the 

 study of the conjugation process is, that in no species of Infu- 

 soria do longitudinal and transverse fission occur together, but 

 every species multiplies either by one form or by the other 

 alone. 



It will not be uninteresting to append some observations re- 

 specting the nucleolus. Siebold seems to have been the first to 

 notice this organ, in Paramecium Bursaria. The researches of 

 Stein and Balbiani, however, have so added to the number of 

 instances of its occurrence, that from thirty to forty may be 

 enumerated. To these Engelmann is able to add a dozen other 

 examples in other species. In Glaucoma scintillans the nucleolus 

 occurs as a small round corpuscle lodged in a hemispherical 

 cavity in the round nucleus. In Frontaria leucas three nucleoli 

 of tolerable size may be brought into view, particularly after the 

 application of water or acetic acid, adherent to the oval elongated 

 nucleus. In Trachelophyllum apiculatum two comparatively large 

 nucleoli are lodged, one in a hollow at each extremity of each of 

 the two oval nuclei. Conchophthirus anodontce (PI. III. fig. 15) and 

 C. curtus have one or two nucleoli lying close to or upon their oval 

 nucleus. A nucleolus also occurs in Aspidisca hjnceus, A. turrita, 

 and A. costata. Vorticella Convallaria and Epistylis flavicans 



