187:2.] 



Modes of Origin of Infusoria §c. 



259 



amongst the granules in some part of the embryo, the alternate contraction 

 and dilatation of which soon showed that it was the contractile vesicle of 

 the infusorium. After a time the embryo began to exhibit movements of 

 quite a different kind (sudden and irregular), no longer checked, but rather 

 increased by slight shocks from without. In one of these sudden plunges 

 the thin enveloping membrane was ruptured, and there entered into the 

 aquatic world a free-swimming and ciliated infusorial animalcule having 

 the characteristics of the species above mentioned. 



Such is the marvellous story ; and the description of other observers is 

 substantially similar. In the particular observation of which M. Pouchet 

 gives the details *, the first rudiments of the eggs began to make their ap- 

 pearance in the pellicle of an infusion of hay on the second day ; on the 

 third day the ovules were distinctly circumscribed, spherical, and -g-jjxr" m 

 diameter ; on the fourth day there was no increase of size, the investing 

 membrane could scarcely be recognized — although there was a distinct 

 gyration of the embryo within it, and in those which were most advanced 

 the contractile vesicle could already be discovered ; on the fifth day the 

 embryos were found to be of the same size, though slightly greenish in 

 colour, and their movements were more irregular and jerking. At this 

 stage the animalcule had assumed a pyriform shape, fine cilia could be 

 seen on some parts of its surface, and the contractile vesicle was most 

 obvious in the midst of minute and densely packed greenish granules. 

 After a few hours more, the buccal cleft, fringed with longer cilia, became 

 obvious, and also the so-called nucleus in the centre of the body. The 

 embryos had by this time somewhat increased in size, so that, after an 

 interval of a few more hours, fully developed specimens of Paramecium 

 viride, ^W 1 in diameter, were swimming about in the solution. 



These observations of M. Pouchet. have been repeated by him over and 

 over again. He has thus seen different forms of Paramedian arise in the 

 pellicle ; and at other times, by steps essentially similar, Kolpodce have 

 made their appearance, The difference between these two forms is indeed 

 quite trivial and unimportant, and wholly unworthy, even from the old 

 point of view, of being regarded as a generic mark of distinction. 



These observations of M. Pouchet have been confirmed by MM. Joly 

 and Musset, M. Pennetier, and others. The former observers declare? 

 that they have watched the evolution of specimens of Kolpoda cucuUus in 

 a pellicle that formed on water in which the contents of a hen's egg were 

 allowed to macerate. In this pellicle there appeared, as they say, "en 

 vertu d'une sorte de cristallisation vitale," the spherical masses of granules 

 constituting " les ceufs spontanes " of Pouchet ; and these in their turn, 

 after a period in which the usual rotation of the embryos within the egg- 

 membrane was observed, gave origin to specimens of the organism above 

 mentioned. On the removal of the first pellicle, it was succeeded by 

 another, in which similar developmental phenomena were repeated. 



* ' Heterogenic,' p. 394. t See Compt. Kend. 1SG0, t, li. p. 934. 



