519 
some (or chromosomes?) behaves during the presynaptic and early 
postsynaptic phases like a typical accessory chromosome (or idio- 
chromosomes?) which determines dimorphism, indicates that here the 
analogue of this element is present, but less highly differentiated and 
in less persistent and easily discernible form. As previously noted 
for mouse, bull and horse [JorDAN‘)|, so in bat a phase appears in 
spermatogenesis comparable to that in forms where definite idiochromo- 
somes obtain. Accordingly, the presumption is strong that an ana- 
logous more elusive element is present subserving a similar function, 
but not revealed at every stage by a clearly defined series of morpho- 
logical pictures. 
Moreover, when one recalls that an accessory chromosome (or 
heterochromosomes) has now been reported for man [GuyYER?)|, kan- 
garoo [NEWMAN and PATTERSON ®)|, opossum [JoRDAN‘)], and guinea 
pig [Stevens°)], it is only reasonable to suppose that its analogue 
should be present in all mammals. If its presence is essential to some 
function (determination of sex?) in some animals, the presumption is 
strong that its analogue is present in some shape in animals where 
this same function is performed. Its apparent absence may simply 
result from our inability to discern it. The appearance of one or 
several phases of idiochromosome history in some instances strongly 
indicates that the remaining phases of the complete process, as seen 
in other forms, also occurs but without leaving recognizable (at pre- 
sent) morphological marks. If the determination of sex in man and 
the opossum demands, or is connected with, an accessory chromosome, 
it is altogether likely, that such element is likewise essential to the 
same process in the bat‘); and that the element above described re- 
presents an accessory chromosome clearly revealed at only one stage 
of its history. 
The minute size of the spermatids renders an attempt at accurate 
observations respecting the series of changes involved in the meta- 
morphoses to a spermatozoon impracticable, and will not be considered 
further at present. 
Regarding the event of synizesis, the following facts controvert 
1) loc. cit. 
2) loc. cit. 
3) Journ. of Morphol., Vol. 21, 1910, No. 3. 
4) loc. cit. 
5) Biol. Bull., Jan. and Aug. 1911. 
6) and even in squirrel where an accessory chromosome can not 
be identified at any stage. 
