rgit] BROW N—LACHNEA SCUTELLATA 291 
exchange of material during synizesis, if not during the resting 
stage. The independence of unit characters in heredity would 
seem to favor the view that there may be an exchange of material 
between chromosomes, for if a given set of unit characters were 
permanently associated with the same chromosomes, we would 
expect to find different characters correlated much oftener than 
they are. If, however, as is generally assumed, the chromosomes 
are the part of an organism which is responsible for the transmis- 
sion of hereditary characters, and if different chromosomes are not 
alike but responsible for different characters, it would be impossible 
for a promiscuous exchange of material between various chromo- 
somes to occur without producing chaos. It would seem more 
likely that the chromosomes are so constituted that only certain 
kinds of material can be fitted into them, so that while chromosomes 
derived from different nuclei may exchange material which is 
responsible for similar sets of characters, they cannot exchange 
material which is responsible for one kind of character for that 
responsible for a different kind. 
The chromosomes at the first division in ie appear to 
approach the poles rather slowly, as anaphase is very abundant in 
sections. The ten chromosomes, formed by the division of the 
five seen at metaphase, are at first grouped at the equator of the 
spindle and give this stage a striking resemblance to metaphase. 
Finally, however, they separate into two groups of five, one of 
which goes to each pole (fig. 39). As the chromosomes approach 
the poles all of them may again divide (fig. 40). The two halves 
of a chromosome do not appear to be connected, but when division 
has just taken place the halves appear to be arranged in pairs, 
the constituents of which usually lie side by side on the spindle. 
It would seem from this that this division is due to a longitudinal 
splitting, and this may be connected with the splitting of the 
spireme seen in the prophase. <A division of the daughter chromo- 
somes as they approach the poles has been described in Gallactinia 
succosa by Marre (27) and GuiLLIERMOND (18). 
After the chromosomes have reached the poles, the fibers which 
connect the centrosomes continue to elongate until they become 
markedly bent. At the same time, breaks are formed on the 
