CELL-NUCLEUS—FERTILISATION 2383 
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 ws 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 
