186 METAMORPHOSES OP MAN 



Nevertheless, it is well to be on our miard against 

 various sources of error. Occasionally, certain organs, 

 or even the entire bodies of Infusoria, are attacked by 

 parasites, which, as they pass away, are sometimes 

 regarded as the offspring of the animal which they 

 are really victimizing.* It seems to me that M. 

 Balbianr's discoveries will necessitate a careful revision 

 of the facts attributed to internal gemmation. It 

 may be that in certain cases, the fragments of the 

 nucleus which have been hitherto looked on as destined 

 to the direct formation of the embryo, pass in reality 

 through the condition of ova, which are afterwards 

 hatched within the substance of the mother, as among 

 all viviparous animals. 



But whether the embryo proceeds directly from 

 the ovary, or results from the transformation of an 

 ovum produced by it, it is quite unlike its parent 

 when it first starts in life, and has to undergo a 

 series of metamorphoses. In what do these con- 

 sist ? Here, unfortunately, we are placed among 

 uncertainties and contradictions, and even what 

 was believed as incontrovertible a few years since, 

 is now either questionable or proved to be erro- 

 neous. 



* Some of these instances of parasitism have been made known 

 by Claparede and Lachmann. Balbiani has also drawn attention 

 to this matter, by a note in which he shows that the Acincta para- 

 sites which become introduced into the bodies of various Infusoria, 

 and especially into those of Paramecia, have been mistaken for 

 embryos formed by internal gemmation. This fact furnished the 

 French naturalist with a new argument against Stein's theory, the 

 reproduction of Infusoria by acineta-forms — which has been justly 

 opposed by Claparede and Lachmann in the " Comptes Kendus'> 

 for 1860. 



