THE CHROMOSOME COMPLEX OF CULEX PIPIENS. 297 
and telophase six thin chromosomes can be seen going to 
each daughter nucleus (PL 20, figs. 11-13). In contrast to 
former experience of larval, pupal, and imaginal material the 
dividing nucleus is most frequently found in the metaphase 
and anaphase stage in the segmenting egg of Culex. 
What takes place in late telophase and in the passage of the 
chromosomes into the resting nucleus recticulum is difficult 
to follow. 
There is thus no difficulty in demonstrating six chromosomes 
in the segmenting nuclei of Culex pipiens — fertilisation 
and the early stages of development are perfectly typical. 
No reduction in the “ Zygote,” as found by Dobell and 
Jameson in Coccidia and Gfregarines, takes place. The 
second hypothesis set forth in the beginning, viz. “ the 
fusion of three pairs of homologous chromosomes at some 
early stage in the life-history, this fusion remaining perma- 
nent throughout later divisions,” most probably explains the 
case. Early prophases show decided tendency of the chromo- 
somes to come out of the reticulum in pairs, full prophases 
show six chromosomes, among which pairing can sometimes 
be detected (PI. 20, figs. 4, 7, 8, 9). As has been shown by 
Stevens and Metz a side-to-side pairing of homologous chromo- 
somes is a characteristic of Dipterous cytology. Metz (2) 
states that Miss Stevens records it in nine species of Muscidae, 
and four species of Mosquitoes, and that he has verified it in 
five of these species of Muscidae, and extended it to eight 
others, in addition to species, of Drosophila. An increas- 
ingly closer proximity of these homologous chromosomes one 
to the other, would produce, eventually, an actual fusion of 
the maternal and paternal constituents, with the result, in- the 
case of Culex pipiens, that in full prophase three, and not- 
six, would be the apparent chromosome number. The three 
chromosomes that appear so persistently in the somatic tissue 
of larvae, pupae, and imagines of Culex pipiens are, there 
fore bivalent in character ; they are really three groups of 
chromosomes, with two in each group. I have not been 
able to trace out more fully the development of this tendency 
