HEREDITY IN THE PROTOZOA 299 
take place independently of the mechanism of Men- 
delian heredity that applies only to genes carried by 
the chromosomes. All that need be said here is that 
as yet no evidence for such influence has been found. 
Second, it remains to be shown whether in ad- 
dition to this somatic selection in the Protozoa, if 
it be such, there may be another form of inheritance 
of the same kind as that prevalent in the. Metazoa, 
based on differences in the chromatin of the proto- 
zoon individual. Let us now examine the evidence 
bearing on this question. 
In the process of conjugation in the Protozoa 
there are phenomena that are often compared with 
those that occur in higher forms before and at the 
time of union of the sperm and egg. Whether 
previous to nuclear interchange there is reduction 
in the number of the hereditary elements and 
whether through interchange there are brought about 
recombinations of elements derived from the two 
parents are questions that can only be settled, as 
in the Metazoa, by a study of characteristics of 
parents (conjugants) and offspring. 
Taking up first the mechanism, that of para- 
mecium may serve for example (Figs. 70 and 71). 
During the time of fusion the macronucleus breaks 
up and its fragments are later absorbed. The 
micronucleus divides, and its daughter halves divide 
again, producing four micronuclei. Three of these 
are scattered in the protoplasm and disappear; one 
again divides into two. One of its halves passes 
into the other conjugant, and there unites with 
