386 BALBIANI; ON SEXUAL 



Frontonia leucas {Bursaria leucas, Ehrb.) and in Ophryoglena 

 flava {B. flava, Ehrb.), and takes place,, perhaps, in ■many- 

 other Infusoria. 



We see, therefore, that while in some Infusoria a nucleus 

 appears, de novo, after each reproductive act, to replace the 

 old ovary vrhich has left no trace of its presence, in others, it 

 is formed anew from those parts of the same organ which have 

 not been concerned in the production of generative elements. 

 '' This re- construction of the sexual apparatus seems then to 

 show that oviparous propagation does not assign a term 

 of limit to the propagation of these beings, as occurs in 

 the case of a large number of other animals, but that they 

 continue to live, still preserving the power of producing 

 fresh generations.'^ It is, indeed, true, that in captivity, in- 

 dividuals which have already reproduced, are more prone to 

 perish than their fellows, but this, M. Balbiani conjectures, 

 may arise from the want of proper food, or some other un- 

 toward condition of the environment. 



Evolution of the Testis. 



When first the nucleolus appears by the side of the female 

 organ, it " presents itself under the form of a minute spherical 

 vesicle, composed, like it, of a membranous wall, and of 

 granular contents. '^ Its early development closely corresponds 

 to that of the nucleus. "There is usually an exact accord- 

 ance as to the mode in which each of these comports itself in 

 the same species. When the egg attains the term of its 

 maturity, without previously multiplying by transverse fission, 

 the male element equally shares every phase of its evolution 

 from the undivided condition; and, in like manner, when the 

 former has given origin, before this period, to a greater or 

 less number of other similar elements, the latter also divides 

 into the same number of secondary parts, each of which 

 corresponds to one of the elements of the first organ. But 

 the multiplication of the two first formed reproductive ele- 

 ments is not always effected simultaneously, and it often 

 happens that the sub-diAdsion of the one precedes by a greater 

 or less interval that of the other. As to the male ele- 

 ment in particular, its multiplication is sometimes completely 

 finished, just when the animal enters on adult age, while that 

 of the eggs is still effected only in part. ^Nlore frequently, 

 however, it is the male element which is less advanced, and 

 which persists sometimes in its rudimentary form up to 

 the time of propagation, then to dinde itself into as many 



