AN EXTRA DYAD AND EXTRA TETRAD IN CAMNULA All 
the normal complex. It is conceivable and, indeed, probable 
that some odd supernumeraries are duplicates of only part of a 
member of a normal chromosome pair, while others are complete 
homologues of such a member. In the former case the extra ele- 
ments must arise through breakage or fragmentation. Some 
evidence along this line is offered by ‘deficiency’ (Bridges, 717) 
and ‘duplication’ in Drosophila (Bridges, 718), although in the 
latter instance fragments do not become free supernumeraries. 
Further evidence is found in the unequal pairs reported by 
Carothers ('13, 717), Voinov (14), Wenrich (’16, 717), and Rob- 
ertson (15). McClung (17, pl. 7, fig. 59, and pp. 530 and 535) 
and Carothers (17, pl. 11, figs. 38 a, 70 d, 70e, and pp. 465, 
485, and 486) have directly observed the breakage of one mem- 
ber of a tetrad in certain first spermatocyte chromosomes of the 
Acrididae. I have seen one instance of the same thing in 
euchromosome no. 3. of Camnula. 
Duplication of an entire member of a chromosome pair may 
result from the abnormal behavior of an element in a maturation 
mitosis. A chromosome pair may fail to synapse or there may be 
a lack of synchronism in the division of the tetrads. In the lat- 
ter case we have the possibility of an element dividing precociously 
in the prophase, or, as suggested by Bridges (’16), division delayed 
until after the cell boundaries have started to form. Wilson (’09 b) 
observed the two members of the idiochromosome pair, presum- 
ably after a failure to conjugate, or a precocious division, passing 
to the same pole in three cells in Metapodius. Doctor Carothers 
has collected some valuable data, still unpublished, in regard to 
this matter. The work of Bridges (13, 714, ’16) has demon- 
strated that a supernumerary present in certain individuals in 
Drosophila is a duplicate of the Y element of. the idiochromosome 
pair, and that it may be the result of: (1) Non-disjunction of the 
two X elements in the female at a maturation mitosis and subse- 
quent fertilization of the XX egg by a Y sperm, or, (2) the forma- 
tion of X Y sperm by non-disjunction of X and Y at the reduc- 
tional division. Aberrant divisions in the first maturation mitosis 
have been observed, too, in the Oenotheras (Gates, ’08 a, ’08 b, 
’09, 711; Gates and Thomas, 714; Davis, 710, ’11). I have found 
