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“chromatin nucleolus” is inexact as well as indefinite since it places 
the structure with the nucleoli, a class of bodies to which it often 
has not even a resemblance in form. Moreover, PAULMIER’s designation, 
“small chromosome”, is an absurd misnomer in the case of the Lo- 
custid cells where the accessory chromosome is as large as five or 
six ordinary ones. In view of the general recognition of the element 
as a chromosome and its still unsettled character, the term “acces- 
sory chromosome” is both suggestive and non-committal, and its use 
is therefore continued. 
According to the results of most investigators the accessory 
chromosome “is characterized 1) by a remarkable uniformity in 
staining power, similar to that exhibited by chromosomes in the 
metaphase; 2) by a continuous peripheral position during the spireme 
stage, at least; 3) by an isolation from the chromatin reticulum and 
a nonparticipation in its changes; and 4) by fission during metakinesis 
after the manner of chromosomes”. These observations are generally 
to be made in the first spermatocyte where the element is most 
plainly manifest. Its identity with a chromosome of the spermato- 
gonia and its failure to divide in one spermatocyte mitoses are facts 
less easily demonstrated, and which have, therefore, less general ac- 
ceptance. 
An outline history of the accessory chromosome as reported by 
the different observers would read somewhat as follows: It is 
first observed in one of the early generations of the secondary 
spermatogonia and thenceforth it is noted as a regular par- 
ticipant in the spermatogonial mitoses. It differs from the other 
chromosomes principally in having a separate vesicle during the pro- 
phase (Surron). At the end of these divisions, it may be seen per- 
sisting in the form of a more or less clearly defined chromosome, 
while the remaining chromatin elements break down to form the spi- 
reme, or equivalent structure (MONTGOMERY, PAULMIER, SUTTON, 
Mc Crung). 
During the long continued prophase of the first spermatocyte, it 
may be found lying at the periphery of the nucleus in the form of a 
sharply defined, darkly staining body. On the establishment of the 
mitotic figure, it takes its place, with varying degrees of con- 
spicuousness, in the equatorial plate of chromosomes and there divides 
(HENKING, PAULMIER, MONTGOMERY). 
When the elements of the second spermatocyte arrange themselves 
ready for division, the accessory chromosome, is again noted, but in 
this instance it fails to divide, and is thus apportioned to but half 
