The Idiochromosomes in Ascaris megalocephala and Ascaris lumbricoides. i23 
of individuals, the idiochromosomes may contimie united to one or the 
other of the ordinary chromosomes, or, on the other hand, there may be 
a normal individual Variation, as Wilson (1909a) shows to be the case in 
the differing results of himself and Montgomery (1906) in regard to 
Metapodius. Wilson completely demonstrates how extensive this Va- 
riation may become in the presence of supernumerary idiochromosomes. 
As given in my preliminary note (Science, 1910) the material upon 
which this paper is based includes many specimens of Ascaris megalo- 
cephala and Ascaris lumbricoides. In the preparation of the testes, fixa- 
tion and staining in Schneider’s aceto-carmine proved the most useful 
method. In addition corrosive subhmate, 5% in 0,5% sodium Chloride 
+ 5% glacial acetic acid, Petrunkewitsch’s fluid, acetic alcohol, 4 parts 
of 96% alcohol + 1 part of glacial acetic acid, and picro-acetic acid were 
employed for fixing, followed by staining in either Mayer’s haemalum, 
Heidenhain’s iron haematoxylin, Kernschwartz, Grenacher’s alco- 
holic borax-carmine, alcoholic hydrochloric-acid carmine, or safranin of 
Bares. Sniears of fertilized eggs, and whole uteri were incubated at 37 °C, 
or allowed to develop at the temperature of the room. Often the stained 
genital tubes, brought into clove-oil and tapped gently under a cover- 
glass gave excellent preparations. Sections of the gonads were 7V2 
while those of the uteri 15, 22 and 30 f^i. 
I desire to thank Professor Boveri for the many courtesies ex- 
tcnded to me, and for his counsel in the course of this work. 
Ascaris megalocephala. 
Herla (1894) describes a small fifth chromosome in this species and 
in some cases where one of the larger chromosomes is shorter than the 
other three, the author suggests that the small element is due to frag- 
mentation from one of the larger chromosomes. In other cases where 
the larger chromosomes are equal in size Herla thinks the eggs might 
be disperm, fertilized by one bivalens and one univalens Sper- 
matozoon. 
In 1908, having observed in an especially large number of the ferti- 
lized eggs of Ascaris megalocephala bivalens, a small chromosome which he 
had previously noted (1899) and thinking it might be a sex-determinant 
Professor Boveri suggested to Miss Boring the investigation of the ques- 
tion. Miss Boring (1909) finds the small chromosome in 32% of the 
343 bivalens eggs examined, and only very rarely in univalens. She 
concludes that the small chromosome is sonietimes due to fragmentation. 
