600 ARTHUR THOMSON, 
or central portion, forming the core round which the sperms 
were developed, atrophied and disappeared ; (2) that the ovum, 
on the other hand, resulted from the increasing preponderance 
of the central nuclear portion, though partly at the expense of 
the peripheral. From this he was induced to formulate a 
general theory of sexual polarities, according to which there is 
in every cellular element an antagonism or different polarity 
between the central nucleus, and immediately enveloping pro- 
toplasm on the one hand and the peripheral protoplasm on the 
other. These polarities are sexual in nature, the central 
polarity corresponding to the female element, and the peri- 
pheral polarity to the male. Every cell in which the two 
polarities are maintained in equilibrium is neuter. The pre- 
dominance of either poiarity conditioned by nutrition, &c., 
makes the cell distinctly unisexual, and the differentiation of 
sexuality is, according to Sabatier, effected by the, possibly 
repeated, extrusion of one of the two substances both origin- 
ally present. The female polarity is centripetal and its 
tendency is to effect cohesion and integration; the male 
polarity is always centrifugal and its tendency is to effect sepa- 
ration and dissolution. The normal cell is thus bipolar and 
ordinary division is inaugurated by a sort of intracellular 
fertilisation between protoplasm and nucleus, the former 
taking the initiative. In the reproductive cell the centripetal 
female polarity is localised in nucleus and central protoplasm 
germinal vesicle and ovum proper in female, blastophore 
sperm in male); the male centrifugal is localised in that 
portion of the protoplasm at the expense of which (according 
to Sabatier) the centrifugal elements (follicular cells, polar 
cells, perivitelline layers, spermatoblasts, &c.) are formed. 
The extrusion of globules from the ovum is thus the elimina- 
tion of male substance. In some cases the process is several 
times repeated, in parthenogenetic ova there ‘is reason to 
believe that it is less. The early ‘ globules précoces” are in a 
sense determinative, their expulsion makes the ovum definitely 
female, though not usually to the necessary extent. Under 
the influence of persisting male substance the nucleus seg- 
