PROPAGATION BY INTERNAL GEEMS. 51 



sule of an oval form, the surface of which presents longitudinal and 

 parallel lines or streaks. Nearly always it soon divides, in the direction 

 of its greater axis, into two or more, frequently into four parts, which 

 continue increasing, independently of each other, in a very irregular 

 manner, and form so many secondary sacs or capsules. At a period 

 which is still nearer that of division, these latter appear to be composed 

 of an extremely fine membrane enveloping a number of small curved 

 bacilla extending from one extremity of the sac to the other, inflated 

 towards the middle, narrowed towards the extremities. It is these 

 which, when seen through the enveloping membrane, give the capsule 

 the striated appearance which is characteristic of it. It also contains a 

 perfectly colourless and homogeneous fluid. 



At the same time, the nucleus has also changed its form and aspect ; 

 it has become rounded and widened ; its substance has become softer, 

 lost its refractive power ; and towards the margins it presents notches 

 which, penetrating more and more deeply into its mass, isolate one or 

 more fragments, in which a sufficient magnifying power enables us to 

 see a certain number of small transparent spheres with an obscure 

 central point. In other cases the nucleus while still almost entire 

 presents this aspect, and then appears as if stuffed with these little 

 rounded bodies, the analogy of which to ovules cannot be doubted in 

 the least. The evolution of the nucleus and nucleolus being identical, 

 and progressing at the same rate in the two coupled individuals, it 

 follows, if we regard the former as an ovary and the second as a testicle 

 or seminal capsule, not only that each of them possesses the attributes 

 of both sexes, but that they fecundate each other. 



As regards this fecundation itself, everything seems to prove that it 

 takes place by means of an exchange made by the two coupled indi- 

 viduals of one or more of their seminal capsules, which pass through 

 the apertures of their mouths, closely applied to each other, from the 

 body of one Paramecium into that of the other ; for very often, although 

 we may not be able to perceive this passage itself, we may detect the 

 moment when one of the capsules already engaged in one of the mouths 

 is on the point of clearing this aperture. 



(107.) Each capsule after its transmission continues to increase in 

 size in the body of the individual which has received it frequently 

 attaining a volume greater than that of the nucleus itself ; but there is 

 never more than one that arrives at maturity 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 from the granulations which mask 

 it more or less while there, it appears under the form of a large ovoid 

 body, the surface of which presents a multitude of parallel striae 

 directed longitudinally, due to the arrangement of the corpuscles con- 

 tained in the interior. Compression, carried so far as to cause its 

 rupture, shows it distinctly to be formed by a membrane of extreme 



