AND THE LOWER ANIMALS. 185 



they were formed.* Modern researches have only 

 substantiated these ideas ; for example, it has been 

 demonstrated by Siebold and Stein, that the nucleus 

 and nucleolus [the reproductive organs according to 

 Balbiani] are, like the other portions of the body, 

 divided between the two offspring, each of which is 

 actually half of its parent. 



The Infusoria are reproduced by external gemmation 

 also, after the fashion of the Hydra ; f and in addition, 

 we find the internal budding which is characteristic of 

 the Aphides. In the Infusoria, as in the insects alluded 

 to, it is upon the egg-producing organ (nucleus), and 

 frequently at its expense, that the embryo is formed. 

 Siebold was the first who pointed this out, J but its 

 entire value was not understood, and indeed the obser- 

 vations were themselves forgotten, when Focke, Colin, 

 and Stein published theirs, which, on the contrary, were 

 received with interest. § From the immense number 

 of memoirs pubhshed by the last-named authors, we 

 are enabled to conclude that this form of reproduction 

 is as general among Infusoria as that of fission. 



"* Saussure was the first who regarded fissuration as a usual 

 method qf reproduction (Dujardin " Histoire des Infusoires "). 

 Trembley made accurate observations on the Vorticella and Stent or, 

 twelve years before (" Etudes sur les Infusoires "). In Messrs. 

 Claparede and Lachmann's work, the details of the physical 

 characters of this mode of reproduction are very precisely stated. 



t This has been long known. The phenomenon was investigated 

 by Spallanzani in 1776, and since his time by a great many observers ; 

 among others by Ehrenberg and Stein. New facts have been added by 

 Claparede and Lachmann, to those discovered by their predecessors. 



% " Helminthologische Beitraege." — Wiegmann's Archives, 1835. 



§ For the entire history of this matter, I can hardly do better 

 than refer the reader to Messrs. Claparede and Lachmann's 

 volume, from which I have borrowed most of the above details. 



