OF THE PEOTOZOA. CILIATA. 331 



often, although we may not be able to perceive this passage itself, we may 

 at least detect the moment when one of the capsules already engaged in one 

 of the months, is on the point of clearing this aperture. Does the exchange 

 which causes fecundation take place with all the capsules in a single copula- 

 tion, or in so many successive copulations with different individuals ? This 

 is a question the solution of which is not easy, and which, to keep within the 

 field of our observations, we shall not attempt to solve at present. 



" However this may be, each capsule, after its transmission, still continues 

 to increase in size in the body of the individual w^hich has received it ; for we 

 have never found any which had attained the limit of their development in 

 individuals which were still coupled. They then frequently attain a volume 

 greater than that of the nucleus itself; but there is never more than one that 

 arrives at matimty at the same time. When, having arrived at this state, 

 it is examined after being pressed out of the body of the animalcule to free 

 it fi'om the granulations which mask it more or less while there, it appears 

 imder the form of a large ovoid body, the surface of which presents a multi- 

 tude of parallel striae dii^ected longitudinally, and due to the arrangement in 

 series of the coi^uscles contained in the interior. Compression, carried so far 

 as to cause its rupture, distinctly shows it to be formed by a membrane of 

 extreme tenuity, and contents, enclosing an innumerable quantity of small 

 fiisifonn corpuscles, of which the extremities are completely lost to sight in 

 consequence of their extreme fineness. As soon as they are free, these little 

 bodies show themselves to be animated by a vacillatory and translatory move- 

 ment, which soon causes their dispersion in the cii^cumambient fluid. These 

 are the spermatozoids of P. Bursaria. Iodine, alcohol, and acetic acid instantly 

 stop their movements ; they are insoluble in the last-mentioned reagent when 

 concentrated, although this dissolves all the other elements of the body, with 

 the exception of the green granules. 



" It is usually from the fifth to the sixth day following the copulation, that 

 the fii'st germs are seen to make theii' appearance, in the form of small rounded 

 bodies, formed of a membrane which is rendered very evident by acetic acid, 

 and greyish, pale, homogeneous, or almost imperceptibly granular contents, 

 in which neither nucleus nor contractile vesicle is yet to be distinguished. 

 These organs do not appear until afterwards. The observations of Stein 

 and F. Cohn have shown how these embryos quit the body of the mother in 

 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 theii' investigations did 

 not reveal to them the ultimate fate of these young animalcules. I have 

 been able to follow them for a considerable time after they detached them- 

 selves from the body of the mother, and have con\-inced myself that, after 

 losing their suckers, becoming surrounded mth vibratile cilia, and obtaining 

 a mouth which first shows itself in the form of a longitudinal fiuTow, they 

 definitely acquired the form of the mother, becoming penetrated in the same 

 way by the green granulations characteristic of this Paramecium, without 

 undergoing any more important metamoqDhoses." 



At the time this first record of his observations was read, M. Balbiani stated 

 that he had collected them from the investigation of six or seven species, but 

 since that period he has pui^sued his observations in several other species, and 

 completed some old ones previously interrupted from want of materials 

 {A. N. H. 1858, ii. p. 439). In his latest paper, he enunciates the remark- 

 able statement that he has been led to regard, in a great number of cases, 

 what nearly all authors have considered to be a spontaneous division in a 

 longitudinal direction, as a sexual union of two indi\iduals. " Very often, 



