66 
EDMUND B. WILSON 
the three small chromosomes are still easily seen in many of the 
nuclei; but they are now pale and diffuse like the bivalents. In 
this respect the third small chromosome differs from a super- 
numerary" of the type described in my former paper, and agrees 
exactly with the m-chromosomes. 
Each nucleus contains at this period a single compact, rounded 
and intensely staining chromatic nucleolus, which is no doubt 
the odd or accessory chromosome (monosome), as in so many 
other formSj^and in addition there is present a conspicuous, rounded 
* This identification is in agreement with that of most observers in recent years. 
A few writers have however disputed the view that the chromatic nucleolus of 
the growth period of the spermatocytes is a chromosome — e. g., Moore and 
Robinson in case of the cockroach ('05), Foot and Strobell in the case of Anasa('07) 
and Euschistus ('09), and Arnold ('08), in case of Hydrophilus. The results of 
Moore and Robinson on this point are opposed by those of Stevens ('05),Wassilieff 
('07), and more particularly by the detailed observations of Morse ('09). Those 
of Foot and Strobell on Anasa are not sustained by the later ones of Lefevre and 
McGill ('08). Among others who have in the past two years adhered to the view 
here adopted may be mentioned Otte ('07), Davis ('08), Boring ('07), Jordan ('08), 
Stevens ('08, '09), McClung ('08), Robertson ('08), Randolph ('08), Nowlin ('08), 
Payne ('09,) Wilson ('096, '09c), Gutherz ('09), Wallace ('09), Gerard ('09), and 
Buchner ('09a). Since I intend to return to the subject hereafter I will take this 
occasion for only brief comment on some of these results, without attempting a 
full review of the literature. 
Moore and Robinson, who have been followed by Arnold (Strasburger, '07, '09. 
expresses the same opinion) also regard the body that is seen passing to one pole in 
one of the maturation divisions ("accessory chromosome") as not a chromosome 
but a ' 'nucleolus." I find it incredible that anyone can hold to such a view who 
reckons squarely with the large existing body of direct and detailed observation 
upon the accessory chromosome itself ; and this view seems to be quite ruled out of 
court by comparative studies on the sex-chromosomes, such for instance as those 
of Payne on Gelastocoris and the reduvioids. I will not enter here upon the maze 
of difficulties regarding the numerical relations of the chromosomes which the 
same view involves, since they have already been indicated by Gutherz ('09), in a 
recent reply to Strasburger. My own preparations, including an extensive series 
of sections and smears especially of Protenor, Lygseus and Pyrrhocoris leave in 
my mind not the least doubt of the identity of the chromatin-(chromosome)- 
nucleolus of the growth period with the odd chromosome (monosome) of the 
spermatogonia, and with the heterotropic or accessory chromosome of the mat- 
uration-divisions. 
Certain writers have seemed to take it for granted that the accessory chromosome 
or ''monosome" is always characterized by its nucleolus-like condition in the rest- 
ing nuclei, not only in the spermatocytes but also in the spermatogonial and other 
