PARAMECIUM 135 



the contractile vacuoles. The two bodies formed by this 

 fission are, like those of Amoeba, asexually produced 

 young, analogous to the buds of certain higher animals of 

 which we shall speak in a later chapter (p. 172). Their 

 development involves not only growth but also the re- 

 modelling of the body, since each of them lacks half the 

 outward organs of the parent, while those which it has are 

 too large for it. In a well-fed culture, division takes place 

 two or three times a day, but if the animals be ill-nourished 

 it is much less frequent, and if they be starved they cease 

 to divide. 



The conjugation of Paramecium is a remarkable process, 

 of a kind found only in this creature and in 

 those which nearly resemble it. In it the 

 animal, though in the absence of body-cells it resembles 

 Amozba and Polytoma, forms in a peculiar way gametes 

 which may be compared with those which are thrown off by 

 the cellular body of the frog. The individuals which form 

 the gametes are exactly alike and resemble normal in- 

 dividuals, except that they are somewhat smaller. As a 

 rule, the process begins during the late hours of the night 

 and lasts till the next afternoon. The details are as follows : 

 Two individuals, which we will call conjugants, 1 lie side 

 by side with their ventral sides together, the endoplasms 

 becoming continuous in the region of the gullets, which 

 degenerate. We may compare this with coition. The 

 micronucleus of each conjugant leaves its normal position, 

 lies free in the cytoplasm, and grows larger. It then 

 divides twice, and three of its four products degenerate. 

 During these divisions the number of chromosomes is 

 halved, as it is in the gametogenesis of the frog (p. 106), 

 though the details of the process differ in the two cases. 

 The remaining micronucleus divides again, this time 

 unequally, the smaller product being the male pronucleus,. 

 the larger the female pronucleus. At this stage we may 

 regard each conjugant as containing two gametes, repre- 

 sented by the two pronuclei. These are analogous to an 

 ovum and a spermatozoon, so that the animal may be said 

 to be hermaphrodite. The true conjugation now takes 



1 They are often alluded to as gametes. This is incorrect. They 

 are not gametes, but parents which form gametes. 



