REPRODUCTION IN THE INFUSORIA. 195 



greyish-yellow tint to their substance, Avhich is then seen to 

 possess consideralile refractory power. "The vitellus, of 

 apparently hoinoi^eneous or finely granular consistence, shows 

 itself after compression to be made up of granules more or 

 less large, loosely adhering together, and united by a mass 

 composed of fine molecular granulations. The germinal 

 vesicle is usually altogether concealed by the vitelline granules, 

 and cannot be recognised. Yet we may sometimes succeed 

 in detecting it by employing successively a very weak solu- 

 tion of caustic potash, which partially dissolves the vitellus, 

 and renders it more transparent, and tincture of iodine 

 diluted with water or weak acetic acid. We may even use 

 for the same purpose, the aqueous solution of carmine in 

 ammonia, which gives to the yolk a roseate tint, more or less 

 deep, and causes the vesicle to appear under the form of a 

 more distinct central spot.^^ 



In Paramecium aurelia an exceptional mode of egg-formation 

 occurs, the details of which, as given by M. Balbiani, derive 

 an additional interest from the very complete manner in 

 which they have been observed. The simply ovoid nucleus, 

 consisting of the usual membrane and granular contents, 

 which this species is seen to possess at the commencement of 

 the sexual act, soon has its surface furrowed by a number of 

 wavy lines, which, becoming deeper and more numerous, 

 quickly divide the yolk-mass into several irregular lobes. 

 These lobes are, at first, very indistinct, and more or less con- 

 fused with one another, but they gradually separate in such 

 a manner, that " at length the entire mass slowly u.nrolls 

 itself into a continuous cylindrical band, sometimes simple, 

 sometimes made up of several branches, variously bent or 

 folded." As yet it exhibits no apparent change in its minute 

 structure. A short interval of repose succeeds, after which 

 the cylindrical yolk-mass breaks up into a succession of 

 large fragments, which in their turn di\dde, and so on, until 

 the whole is resolved into a considerable number of rounded 

 corpuscles, varying in diameter from "010 mm. to "014 mm. 

 Some of these, under acetic acid, display a clear centre 

 surrounded by granulations, others granulations only. 

 Meanwhile the membranous envelope, obliged to keep 

 up with its contents, becomes so excessively attenuated, 

 that its presence is no longer susceptible of actual demon- 

 stration. 



Besides the corpuscles just mentioned, there are others 

 which, about this time, make their appearance within the 

 ovary. Their number is usually four, rarely two or eight. 



VOL. 11. NEW SEK. O 



