124 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 
subsequent development of a perinuclear zone, as described above. 
The nucleus then commences to grow and faint radiations can some- 
times be seen extending from the perinuclear zone into the surrounding 
cytoplasm. 
During immersion in the hypertonic solution there are no apparent 
changes beyond a slight reduction of the clear zone of hyaloplasm 
surrounding the nucleus. 
After the eggs are put back into normal sea-water the internal 
changes resulting in the first cleavage follow each other in quick sue- 
cession. The first change noticed is an increase in the development of 
the perinuclear zone, followed by further growth of the nucleus. Mean- 
while, the meshwork of chromatin becomes coarser and more aggre- 
gated together and the nucleolus gradually disappears. This stage 
is succeeded by a reduction of the perinuclear zone together with its 
radiations. 
About half an hour after transference to normal sea-water, from 
one pole of the nucleus a definite aster begins to develop, its rays 
focusing in a more or less indistinet centrosome situated on the nuclear 
membrane! By division of the centrosome a typical amphiaster is 
formed in the nuclear area and as it develops the nuclear membrane 
disappears. At the same time the chromatin assumes the form of 
a spireme, which subsequently breaks up into about 18 long and 
slender chromosomes. At this stage it is impossible to clearly dis- 
tinguish their number, but, as the chromosomes are graduaily drawn 
into the equator of the cleavage amphiaster, they shorten consider- 
ably and become quite distinct by the time that the equatorial plate 
is formed. 
At this stage we have made numerous counts of the chromosomes 
and invariably found it in the neighborhood of 18, which is half the 
number that is normally present in this species. 
This behavior is very similar to the one found in the egg 
after fertilization by sperm. 
1[t may be well to call special attention to the fact that the centrosomes and. 
astrospheres are not formed while the eggs are in the hypertonic solution but 
some time after they are put back into the normal sea-water. Only if the eggs 
remain too long in the hypertonic sea-water centrosomes and cytasters may form 
while the eggs are in the hypertonic sea-water, not, however because they are in 
this solution but in spite ofit. The hypertonic solution allows the internal process 
leading to the formation of astrospheres to go on for some time. This led to the 
erroneous idea that the hypertonic solution was the direct cause of the formation 
of centrosomes and astrospheres. 
