580 
GEOFFEEY SMITH. 
erroneous, especially by E. B. Wilson and his pupils. Wilson 
(4) has shown that although the dimorphism of the sperma- 
tozoa does occur, and is, indeed, a frequent phenomenon 
among insects, yet that where an “ accessory ” chromosome 
is present in the males it is due to half the spermatozoa con- 
taining one chromosome less than the eggs, while those with 
the “^accessory” chromosome contain the same number as 
the eggs. It is therefore impossible to say that the sperma- 
tozoa with the accessory chromosome give rise to males, as it 
is evidently those without the accessory chromosome which, 
in conjunction with an egg, produce an animal with an odd 
number of chromosomes, i.e. a male. This fact has pre- 
vented Wilson hitherto from accepting McClung’s simple 
interpretation, since he is convinced that the sex-character 
must be represented by a definite chromosome in the cell. 
Of course, if we are content to give up the idea of the sex- 
character being necessarily represented by a definite chromo- 
some, an idea which, indeed, has not vei’y much to support it, 
McClung’s explanation would still hold, except that the male- 
producing spermatozoa would be those without the accessory 
chromosome, while the female-producing spermatozoa would 
be those that possessed it. Professor Wilson, however, will 
not readily accept this, and he has endeavoured to get over 
the difficulty by framing several different theoi’ies of sex of 
very great complication. The latest of these theories not 
only assumes a great complication of gametic representatives, 
but also involves selective fertilisation, so that it belongs to 
the same category as Castle’s theory and need not be dis- 
cussed further at present. 
During the years 1904-6 I was occupied at Naples in 
studying the effect of the parasitic Cirripede Sacculina on 
its host, a species of spider crab (Inachus), and from this 
study I was led shortly to formulate a Mendelian theoiy of 
sex. As the result of the examination of many thousand 
specimens of the crab at various stages of infection, I con- 
cluded that whereas the males, under the influence of the 
parasite, were capable of assuming all the female secondary 
