CELL-NUCLEUSFERTILISATION 233 



for each of the two daughter nuclei receives 

 entire chromosomes, but of course the original 

 number, now shared between two nuclei, is 

 really reduced in each of them to one-half of 

 what it originally was in previous nuclear 

 divisions. 



It will be remembered that prior to the 

 temporary union of the chromosomes to form 

 the pairs, each one of them showed indications 

 of longitudinal fission. It is of special interest, 

 then, to find that immediately on the form- 

 ation of the daughter nuclei, in the way just 

 described, this fission becomes operative. For 

 a second division supervenes in each daughter 

 nucleus, and so four nuclei are produced. The 

 reduced number of chromosomes in each 

 nucleus is, of course, maintained. Indeed, it 

 invariably happens that all nuclei which are 

 derived from one in which reduction has 

 occurred only possess the halved quantity. 

 It is not until the union of the sexual cells 

 takes place that the original number is again 

 restored. 



The term meiosis has been applied to this 

 process of reduction, and meiosis occurs in 

 every animal and plant which reproduces 

 itself sexually (with possible exceptions, per- 

 haps, in some of the lowest and most aberrant 

 types). Not only so, but even the details of 

 the process are remarkably similar in the 

 many species of animals and plants which 

 have been studied. ^ 



Now it is hardly possible that a process so 



