CHROxAIOSOMES, HEREDITY AND SEX. 
487 
Chromosomes, Heredity and Sex : A Review of 
the Present State of the Evidence with regard 
to the Material Basis of Hereditary Trans- 
mission and Sex-Determination. 
By 
]>oiic:ist€r, Sc.I>., 
Fellow of King’s College, Cambridge. 
With 4 Text-figures. 
It is now rather over ten years since the hypothesis was 
first put forward that the segregation of Mendelian allelo- 
morphic characters is caused by the pairing in synapsis ” of 
chromosomes of paternal and maternal origin, and their sub- 
sequent separation into different gametes ( 58 , 59 , 64 ). At 
about the same time, the discovery of an accessory chromo- 
some in the spermatocytes of several Orthopterous and 
Hemipterous insects, which passes undivided into half the 
spermatids, led to the suggestion that this body was a sex- 
determiner ( 31 ), and shortly afterwards Castle ( 13 ) put forward 
the hypothesis that sex-determination is due to a pair of 
Mendelian factors, which segregate in gametogenesis in such 
a way that every germ-cell bears one or other. In this paper 
it is not proposed to review the earlier work, nor to give an 
account of all the papers which have added to our knowledge 
of the subject, but to summarise some of the more important 
lines of evidence which have become available in the last few 
years, so as to show as far as possible the present state of our 
knowledge.^ Further, it is not proposed to deal at all com- 
pletely with the various theoretical speculations to which the 
matter has given rise, except in so far as is necessary for the 
^ References are given on p. 517 to papers which may be regarded as 
typical. 
VOL. 59, PART 4. NEW SERIES. 
32 
