320 | T. H. Morgan 
portant conclusion would remain, that the preliminaries of sex- 
determination—and possibly therefore its cause in the sense of 
inaugurating a sequence of events—takes place in the egg of 
Hydatina before the maturation of the eggs. ‘These preliminaries 
involve moreover the question of sex-determination and not simply 
sex-production. 
Lenssen’s observations on the maturation of the egg do not 
seem to be entirely correct, although his general conclusions that 
the same number of chromosomes are present in the male egg 
and in sexual eggs, and that double that number are found in the 
parthenogenetic eggs, is sound. ‘The recent results of Whitney 
place this conclusion on a surer basis. Whitney points out that 
the parthenogenetic egg extrudes one polar body, the male egg two; 
that the sizes of the individual chromosomes in the male egg and in 
the sexual egg are twice that of the chromosomes in the partheno- 
genetic egg. ‘These facts leave little room to doubt that a reduc- 
tion in the number of the chromosomes of the male egg takes place 
preparatory to the formation of a male. Hence the possibility of 
fertilization of such an egg becomes intelligible, since the reduc- 
tion is a preparatory step to fertilization in the sexual egg. The 
fact too that the reduction occurs in the male egg (that develops 
parthenogenetically) shows that the entrance of the sperm in the 
sexual egg has nothing whatever to do with the determination of 
reduction in that egg, and this substantiates the conclusion reached 
above that the preliminaries for sex determination go on irrespect- 
ive of the presence of the sperm. In this instance, however, the 
process only involves reduction that is common to both male and 
sexual female eggs. 
Another fact emerges from Whitney’s observations—the male 
egg, as well as the parthenogenetic egg, is produced in the presence 
of all of the chromosomes— as in the phylioxerans. So, too, is the 
sexual egg, plus, however, the chromosomes of the male—which 
proves too much for the chromosome view, unless the compact 
sperm be assumed to have already become functional. But this 
assumption cannot be made for the phylloxerans. 
If, after reduction and the extrusion of two polar bodies, in the 
male rotifer, we suppose that the male has half the total number of- 
