The Idiochromosomes in Ascaris megalocephala and 
Ascaris lumbricoides. 
By 
Charles Lincoln Edwards. 
(Aus dem Zoologischen Institut Würzburg.) 
"With plates XXI and XXII. 
The ‘‘accessory chromosome” discovered by Henking (1891) in Pyr- 
rhocoris apterus, has been foimd as an unpaired idiochromosome^) or a 
group of idiochromosomes, in many other hemiptera and insects, as well 
as in echinoids (Baltzer, 1909), and in nematodes. McCluxg (1902) is 
the first to associate the idiochromosome with the production of sex, under 
the belief that when a Spermatozoon possessing this element fertilizes an 
egg, a male is produced. In certain forms, Stevens (1905) and Wilson 
(1906) demonstrate two idiochromosomes in the female similar to the 
single one characteristic of the male. Hence contrary to WcClung, 
Wilson (1905) concludes that in these forms fertilization of the egg, which 
itself possesses an idiochromosome, by a Spermatozoon without an idio- 
chromosome produces the male thns characterized by an odd idiochromo- 
some. The Spermatozoon carrying an unpaired idiochromosome, ferti- 
lizes an egg also with a similar unpaired element, thus producing a female 
with a pair of idiochromosomes. 
Foot and Strobell (1907) and, accepting their conclusions, Arnold 
(1909) are skeptical of the existence of sex-producing chromosomes. Le- 
FEVRE and Mc Gill (1908), and Wilson (1909a and other related papers), 
have demonstrated that the conclusions of Foot and Strobell are er- 
roneous. In cases of disagreement concerning the same spec’es sometimes, 
it is possible, as in Ascaris megalocephala, that even in a large majority 
^) The terminology used in this paper is that proposed by Wilson, 1909. 
