The Idiocliromosomes in Ascaris megalocephala and Ascaris lumbricoides. 427 
haps may illustrate a normal Variation which rnight be expected in the 
number of chromosomes, as well as in their form and size, eorresponding 
to the variations which occur in the characters of the individual which 
have their ontogenetic source in these chromosomes. 
This type of sex-determinant has some similarity with that of Gelas- 
tocoris ( Galgulus) ociilatus described by Payne (1908), but differs froni it 
f undamentally in that instead of the pentad element dividing into differen- 
tial groups of four and one, in Ascaris lumbricoides all five constituents 
of the group go to one daughter cell. The conditions in Ascaris lumbri- 
coides are not exactly parallel to any of the types of Wilson (1909). We 
have here as the fertilization formula: 
Egg 24 (including bi) + Spermatozoon 19 = zygote 43 (including 5i), 
(cT)- 
Egg 24 (including bi) + Spermatozoon 24 (including bi) = zygote 48 
(including 2 ( x bi), ( Q ). 
Zoological Institute, University of Würzburg, March 1910. 
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