330 GENEBAL HISTOEY OF THE INFUSORIA. 



But under the influence of conditions of which we are still ignorant, the 

 species propagates itself in a very different manner, and in the midst of phe- 

 nomena far more complex than those which preside over the multiplication 

 by fissiparity. In this new mode we shall see the actual anatomical signifi- 

 cation of the nucleus and nucleolus, the ftmction of which, if we except the 

 di\ision of the former of these two organs in the act of spontaneous division, 

 has hitherto been perfectly passive. It is, in fact, at their expense that the 

 male and female reproductive elements which characterize this mode of 

 propagation are formed. 



" When the period arrives at which the Paramecia are to propagate with 

 concourse of the sexes, they are seen assembling upon certain parts of the 

 vessel, either towards the bottom, or on the walls. The copulation is always 

 preceded by certain preliminaries which are very cimous to observe, but upon' 

 which we cannot dweU here. Soon they are found coupled in pairs, adherent 

 laterally and as it were locked together, with the similar extremities turned 

 in the same direction, and the two mouths closely applied to each other. In 

 this state the two conjugated individuals continue moving with agility in the 

 liquid, and turning constantly round theii' axis. There is nothing, before the 

 copulation, to announce the considerable changes which are about to take 

 place in the nucleus, and the nucleolus which accompanies it. It is diuring 

 the copulation itself, of which the duration is prolonged for five or six days or 

 more, that their transformation into sexual reproductive apparatus takes place. 

 " The nucleolus has undergone a considerable increase in size, and has 

 become converted into a sort of capsule of an oval form, of which the sm^face 

 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 

 foui', parts, which continue increasing independently of each other, and in a 

 very irregular manner, and form so many secondaiy sacs or capsules. At a 

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

 of an extremely fine membrane, enveloping a bundle of small, curved baciUa, 

 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 a23pearance 

 which is chai'acteristic of it, and which even exists in the nucleolus at almost 

 all the other periods of the life of the Infusorium. 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 and lost 

 its refractive power, and towards its margins it presents notches, which, 

 penetrating more and more deeply into its mass, isolate one or more frag- 

 ments, in which a sufficient magnifying power enables us to see a certain 

 number of small transparent spheres with an obsciu'e central point. In other 

 cases the nucleus, whilst still almost entire, presents this aspect, and then 

 appears as if stuffed \sith these little rounded bodies, the analogy of which to 

 o\TLles 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 

 indi^T-duals, it follows, if from this moment we regard the former as an ovaiy, 

 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, 

 and serve at the same time as male and female. As regards this fecimdation 

 itseK, everything seems to prove that it takes place by means of an exchange, 

 , made by the two coupled individuals, of one or more of their seminal capsules, 

 which pass, through the apertures of the mouths closely applied against each 

 other, from the body of one Paramecuim into that of the other ; for, very 



