OF CILIATED INFUSORIA 263 



fact formed, as they seem to be, as a result of transformations 

 occurring in the immature ova. 



(f) On the Heterogenetic Origin of Certain Ciliated In- 

 fusoria from the Eggs of a Rotifer.^ 



The weight of preconceptions against the possibility of the 

 occurrence of Heterogenesis has hitherto been so strong as to 

 have made it almost impossible to obtain any adequate considera- 

 tion for the actual evidence adduced in favour of this or that 

 alleged instance. But of late, preconceptions in the domain of 

 physics and chemistry have received severe shocks, and when we 

 are told that a so-called '' element " is daily being transformed 

 and another is actually originating from it, there appears more 

 chance of attention being paid to the alleged existence of phe- 

 nomena in the organic world which would seem to be but the 

 carrying on into a higher platform of the familiar phenomena 

 known as allotropism and isomerism. 



Hitherto, alleged instances of heterogenesis have, without 

 adequate consideration of evidence, been almost always assumed 

 to be results of "infection," but it seems clear that in the cases 

 with which the present section is concerned, any such explanation 

 is quite impossible in regard to one of the cases, at least, in which 

 we have masses of living matter so large that they average 1/200 

 of an inch in diameter, being converted, in the course of three days, 

 into great Ciliated Infusoria of equal bulk. 



We have now to consider two sets of heterogenetic transforma- 

 tions occurring in the great eggs or 'gemmae' of one of the 

 largest of the Rotifers, namely, (i) the transformation of the entire 

 contents of a Hydatina egg into a single great Otostoma ; and (2) 

 the segmentation of the Hydatina egg into 12 to 20 spherical 

 masses, and their development sometimes into embryo Vorticellae, 

 and sometimes into embryo Oxytrichae. 



■ This section is a reproduction, with several additions, of a paper in ' The 

 Proceedings of the Royal Society ' (B., Vol. 76, 1905). In compliance with the 

 wishes of one of the Referees I was asked to alter the title, and in order not to 

 run the risk of the communication being rejected I assented to a change. When 

 sent in it bore the same title as this section, but before it was read the title 

 became " On the Occurrence of certain Ciliated Infusoria within the Eggs of a 

 Rotifer, considered from the Point of View of Heterogenesis." That which 

 appears in the ' Proceedings ' is little more than an abstract (illustrated) of the 

 memoir that was sent to the Royal Society, and which is now preserved in its 

 Archives. 



