52 INFUSORIA. 



tenuity containing an immense number of minute fusiform corpuscles, 

 the extremities of which are imperceptible on account of their extreme 

 fineness. As soon as they are free, these little bodies exhibit a vacil- 

 latory and translatory movement, which soon causes their dispersion in 

 the circumambient fluid. These are the spermatozoids of Paramecium 

 Bursaria. 



(108.) It is usually from the fifth to the sixth day following the 

 copulation that the first germs are seen to make their appearance, in 

 the form of small rounded bodies formed by a membrane which is' 

 rendered very evident by acetic acid, and containing a greyish, pale, 

 homogeneous or almost imperceptibly granular matter, in which neither 

 nucleus nor contractile vesicle is yet to be distinguished : these organs 

 do not appear till afterwards. Stein and F. Cohn have shown that 

 these embryos quit the body of their parent under the form of Acinetce, 

 furnished with knobbed tentacles (true suckers, by means of which 

 they remain for some time still adherent to the mother, deriving their 

 nourishment from her substance) ; but their investigations did not re- 

 veal to them the ultimate fate of these young animalcules. M. Bal- 

 biani was able to follow them for a considerable time after they had 

 detached themselves from the parent animalcule, and convinced him- 

 self that, after losing their suckers, becoming clothed with vibratile 

 cilia, and obtaining a mouth, which first shows itself in the form of 

 a longitudinal furrow, they definitely acquired the form of the mother, 

 becoming filled in the same way with the green granulations charac- 

 teristic of this Paramecium, without undergoing any more important 

 metamorphoses. 



M. Balbiani * did not succeed in witnessing the deposition of the ova, 

 but he thinks it very probable that they escape by the anus or by some 

 neighbouring aperture. In Stylonychia he observed them to collect in 

 the posterior part of the body and diminish gradually in number from 

 the first or second day after copulation, at which period a round pale 

 body begins to make its appearance in the centre of the animalcule, which 

 becomes constricted in the middle and reconstitutes the double nucleus. 



(109.) The Infusoria would seem to be destitute of copulatory 

 organs. In most cases sexual intercourse is effected by simple juxta- 

 position of the mouths of the two animalcules. In the Oxytrichina the 

 union is more intimate, and goes so far as to constitute a true solder- 

 ing of the two individuals for more than two-thirds of the anterior part 

 of their length. Any one who had not witnessed all the phases of this 

 remarkable copulation would necessarily regard this state as a case of 

 longitudinal division proceeding from behind forwards ; but the con- 

 comitant changes of the internal organs cannot leave the least doubt as 

 to the signification of this act. 



* " On the Generative Organs of the Infusoria," Ann. Nat. Hist. ser. 3. vol. ii. 

 p. 443. 



