Ou Morphological Ditference of the Chroiuosomes of Ascaris megaloceph. 69 
It is difficult to decicle in tbe Spermatozoon whether these chro- 
mosomes are approximately eqnal in volume or whether they possess 
a constant size difference; but the study of a large number of free 
spermatozoa indicates that the two are in most cases slightly dissi- 
milar in volume, though I canuot he positive that they are constant- 
ly so. But when the sperm has reached the ceutre of the egg, 
and the latter has the first polar spindle at the surface, the sperm 
chromosomes are mueh larger as well as more separated (PI. 7, 
Fig. 67 — 71), and are now in all cases ocularly separable, as noted 
by Zacharias (1887), Carnoy (1886; and Büveri (1888). What has 
not been observed before is that at this stage the two sperm chro- 
mosomes can be seen to be of constantly different volume, though 
not of constant different form. And at the time of the second polar 
spindle when the sperm chromosomes are already loosening to form 
the male pronucleus, they are also always somewhat different in 
volume (Fig. 53, 72). 
Therefore we conclude that the two chromosomes introduced by 
the sperm into the egg are constantly of different volume. 
2. The Chromosomes of the Polar Spindles. 
It is well known that the first polar spindle contains two quadri- 
partite chromosomes, or two tetrads, that the second has two dyads 
and that the second polar body as well as the egg each receive two 
single chromosomes. Of each dyad of the second polar spindle one 
chroinosome is given out into the second polar body while the other 
remains in the egg, therefore if the two dyads are constantly une- 
qual in volume the two chromosomes left in the egg must also be 
so. I have studied the second polar spindle rather than the egg 
chromosomes at the completion of this stage simply because I had 
more preparations of the stage of that second spindle. Figures 53 — 65, 
PI. 7, represent views of second polar spindles, all seen obliquely so 
as to Show the dyads with the greatest distinctness. It will be no- 
ted that in all of them the two dyads are of constant unequal volume. 
Therefore we conclude that the two chromosomes left in the 
egg at the dose of the maturation divisions are constantly of une- 
qual volume. 
3. The Chromosomes in the Prophases of the First Cleavage. 
Chromosomal boundaries are ocularly indistiuguishable during 
the rest stage of the pronuclei, a fact, however, that in no way dis- 
