THE BEGINNINGS OF LIFE. 



293 



cess of fission in Oxytricha, says ^ that ^ some hours ' 

 are required for its completion in large individuals. 



Though the development of <^ova' in the Infusoria 

 by a sexual process of generation seems now to be 

 generally accepted, on the faith of the recent researches 

 of Balbiani and those of MM. Claparede and Lach- 

 mann, no appeal can be made to such a process of re- 

 production in order to account for the rapid appearance 

 of multitudes of Infusoria in organic solutions. Even 

 those observers whose labours have tended to establish 

 the reality of the process, do not pretend that it is an 

 ordinary mode of multiplication. On the contrary, they 

 maintain that it is an extraordinary method of increase 

 to which the animal resorts occasionally under the 

 pressure of adverse circumstances 2. The rate of in- 

 crease, also, could only be extremely slow by this 

 method, since the animals remain in contact for five 

 or six days, and it is not till a further lapse of two or 

 three days that the ^ ova ' obviously begin to make their 

 appearance =3. Balbiani's observations were principally 



^ 'Ann. des Sc. Nat.' 1853, p. 122. 



' When speaking of the process of fissiparous division, M. Balbiani 

 says (loc. cit. p. 1194) : — ' Nous avons effectivement constate que ce mode 

 de propagation avait des limites et se terminait invariablement de I'une 

 des trois manieres suivantes : ou part la mo;"t naturelle et presque simul- 

 tanee de tous les individus appartenant a une meme cycle, ou par le 

 retour de la generation sexuelle indiquant la fermeture d'un de ces cycles 

 et le commencement d'un cycle nouveau, ou enfin par le phenomene de 

 I'enkystement.' 



5 'Journal de Physiologic,' 1858, torn, i p. 346. The process is 

 doubtful in nature ; and from the absence of all sexual organs in the two 



