A Small Cliromosome in Ascaris megalocephala. 
125 
we may couclude from the bastard eggs tbat the small chromosome 
siirely comes from the Spermatozoon in some cases, and possibly from 
the egg in others. 
That the small chromosome comes in many cases from the 
Spermatozoon is proved by the conditions observed in certain abnormal 
eggs. In one hivalens worm, [nearly half of the eggs showed an 
abnormality not before described, namely, after the formation of a 
normal first polar body, all the chromatin of the second polar spindle 
was extruded in the second polar body, so that this contained four 
elements instead of the typical two. These eggs therefore have no 
female pronucleus. In accordance with this, in all the equatorial 
plates of these abnormal eggs, there are only two chromosomes, 
which must arise from the male pronucleus. In 15 out of 29 eggs, 
a small chromosome was observed (Fig. 7) and here it is sure to 
be a paternal element. 
In another worm a single egg was found with only two chromo- 
somes beside the small one (Fig. 8). Here the first polar body was 
present, and the second polar body contained the normal two rods, 
but there was no spindle. This is probably a later stage of a case 
such as Boveri mentions in Zellenstudien II, p. 169 (’88), where only 
one pronucleus with two chromosomes is present, and yet the polar 
bodies are normal. The Spermatozoon in this case had entered the 
egg, but developed no further, so that the male pronucleus is the 
one lacking. Judging from the stage in which the pronucleus is 
found, two distinct centrosomes and spheres should be developed, 
but there is no trace of them in this egg, a fact that Boveri has 
used as the chief argument that the centrosomes arise from the Sper- 
matozoon. Prof. Boveri has told me that since then, he has seeii 
several similar cases, but with the difference that the Spermatozoon 
which in the first case had penetrated the egg, but developed no 
further, could not be found at all. All the eggs were alike in that 
the polar bodies were normally formed, that instead of the normal 
first cleavage number of chromosomes there were here only half as 
many and that although in all these cases, the chromosomes lay free 
in the protoplasm, there was no trace of a spindle or aster. Prof. Boveri 
concludes from this, that the mere contact of the Spermatozoon with 
the unripe egg, without its entering is sufficient to start the matu- 
ration processes and make the female pronucleus develop as far as 
the dissolving of its membrane. After that, the development must 
stop, for the centrosomes from the Spermatozoon are lacking. The 
