452 LAWS OF MULTIPLICATION. 



occurs a process of conjugation akin to that which th( 

 Protophyta exhibit — a coalescence of the substance of two 

 individuals to form a germ-mass. This has been alleged 

 more especially of Actinophrys. If this statement should 

 be proved true,* then of the minute forms that appear to be 

 more animal than vegetal in their characters, some have a 

 mode of sexual multiplication by which the parents are 

 sacrificed bodily in the production of a new generation. 



Among small animal aggregates of the second order, the 

 first to be considered are of course the Ccelenterata. A Hydra 

 occasionally devotes a large part of its substance to sexual 

 genesis. In the walls of its body groups of ova, or sperma- 

 tozoa, or both, take their rise; and develop into masses 

 greatly distorting the creature's form, and leaving it much 

 diminished when they escape. Here, however, gamogenesis is 

 obviously supplementary to agamogenesis — the immensely 

 rapid multiplication by budding continues as long as food is 

 abundant and warmth sufficient, and is replaced by gamo- 

 genesis only at the close of the season. A better example 



* To this passage Prof. MacBride appends the remark : — " This is quite 

 proven now, and the statement as it stands is quite correct ; but far better 

 and more minutely worked out cases are to be found amongst the Infusoria. 

 In Paramecium for example, there are normally present a large macro- 

 nucleus and a small micronucleus lying alongside of it. When two indi- 

 viduals adhere preparatory to conjugation, the macronucleus breaks up into 

 fragments which are absorbed : the micronucleus — which has some time pre- 

 viously divided into two — begins to break up further and eventually forms 

 eight bodies ; all of these except one disappear ; this last piece then divides 

 into two ; of these two one represents a male genital cell, for it passes over 

 into the body of the other Paramecium and fuses with one of the two corre- 

 sponding nuclei there ; thus each of the two individuals which adhere 

 fertilizes the other. The two individuals then separate and the nucleus 

 (result of fusion of male and female nuclei) in each divides into four. Of 

 these, two move to one end of the animal and two to the other. The 

 animal then divides into two transversely — each of the products thus hav- 

 ing two nuclei which form the micro- and macro-nucleus of it. Thus it 

 appears that the function of sexual union is simply to give increased vigour 

 to all the vital processes including fission. Since as mentioned above (p. 

 443) if it is prevented, the products of fission are eventually unable to feed 

 themselves." 



