i8a Education through Nature 



the middle, and thus nuclear division is complete. Con- 

 striction divides the cell-body into two equal parts, which 

 separate and form two new Paramecia. A swarm of 

 Paramecia, well supplied with food, will continue to mutli- 

 ply by binary fission for many generations. 



Prior to conjugation the individuals move hither and 

 thither in a rapid and excited manner, as if in search of 

 one another. After a while they come together in couples 

 and conjugate. Two individuals become attached to- 

 gether mouth to mouth, and are closely united by fusion. 



Usually the process of conjugation begins during the late 

 hours of night and the early hours of the morning, and 

 lasts till late in the following afternoon. The first conse- 

 quence of conjugation is that the micronucleus of each 

 gamete goes through a stage of evolution, which doubles 

 its diameter. It also undergoes change of shape, becoming 

 first elongated, then spindle shape, and then doubled up 

 to form a crescent, while its chromatin granules are aggre- 

 gated in rows to form longitudinal fibrils. But it eventually 

 resumes its original ovoid condition. This structure, in- 

 creased as it is to twice .its former diameter and eight times 

 its original volume, passes through mitosis and divides 

 into two, and each product of division immediately under- 

 goes mitosis and again divides, so that there are now four 

 micronuclei. Meanwhile the macronucleus has undergone 

 no change. The four micronuclei in each gamete are of 

 equal size, and all of these begin to prepare for a new 

 division by elongating to form fibrous spindles; but only 

 one and it is always the micronucleus which happens to 

 be nearest to the mouth passes through the further stages 

 of mitosis and divides. The three others are arrested at 

 the spindle stage, and then degenerate and are absorbed. 

 The surviving micronucleus in each gamete completes 

 its division so that each gamete has two micronuclei and 

 one as yet unaltered macronucleus. In each gamete one 

 of the micronuclei is placed close against the mouth, called 

 the female and male pronuclei. Both elongate and form 

 fibrillated spindles, and then the transference of micro- 

 nuclear material. The transference of nuclear material 

 has now been effected, and the gametes, which have dimin- 

 ished in size, shortly afterwards separate from one another, 



