1 00 BALBIANIj (>\ SKXUAL 



all, for, alt'aough its actual presence still remains to be 

 demonstrated in by far the majority of Infusoria, yet the 

 sexual union of these last is not known to differ in any 

 essential respect from that of the others. Its position, also, 

 Avould seem to be equally constant, namely, in the ventral 

 surface of the body, between the mouth and the anterior ex- 

 tremity. Stentor cannot be said, to present an exceptional 

 case, if we admit, with M. Balbiani, the homology between 

 the 'front' of these animalcules and the large depressed 

 region about the mouth in other InfusoriS.. 



With regard to Infusoria of the second great category, 

 among which the mouth is situate at the anterior pole of the 

 body, M. Balbiani has nothing to say on the subject of their 

 genital aperture, save the fact that in Coleps, sexual union 

 seems to be effected by the large orifice which occupies this 

 extremity. 



It would be an error to conclude that M. Balbiani has 

 been the first to witness the act of copulation among the 

 Infusoria. This had, indeed, already been done by others, 

 who, so far, however, from rightly interpreting the facts be- 

 fore them, mistook the pairs of animalcules thus found 

 united for a single individual undergoing development by 

 longitudinal fission. And many Infusoria were said to divide 

 indifferently, either in a longitudinal or transverse direction. 

 Ehrenberg's figures, so often copied, representing Chilodon 

 cucullulus in both these supposed states of fission, must be 

 familiar to many of our readers. But, although longitudinal 

 division occurs in some Infusoria, more particularly the 

 Vorticellina, yet, in by far the majority of the class, voluntary 

 fission seems always to be effected transversely. While the 

 changes induced thereby in the conditions of the sexual 

 organs, are very different from those determined by repro- 

 ductions. 



Many subsidiary phenomena of great interest either ac- 

 company or precede the copulatory act, among the several 

 tribes of Infusoria. Into these, want of space forbids us now 

 to enter, for it would scarcely be just to maim, by imperfect 

 quotations, the complete descriptions of M. Balbiani. Our 

 readers should consult for themselves the interesting account 

 which he has given of the sexual act in the Oxytrichina, 

 which, without tlie aid of his excellent illustrative figures, we 

 could hardly hope to render intelligible. In these a most 

 curious and complete series of changes occurs, and a very 

 intimate degree of union establishes itself between the two 

 animals, which lose a number of their appendages, shiftine- 



