ARTIFICIAL PARTHENOGENESIS AND OXIDATIONS 125 
In naturally fertilized eggs a distinct aster (cleavage aster) appears 
at one pole of the nucleus, its rays centering in a clear area which repre- 
sents a diffuse centrosome. This area divides and the two halves 
move apart until they come to lie at opposite sides of the nucleus and 
form the poles of a typical amphiaster which is developed in the 
nuclear region. Meanwhile the chromatin assumes the form of a 
spireme, which breaks up into 36 chromosomes that arrange themselves 
about the equator of this amphiaster to form a nuclear spindle. In 
the chemically fertilized eggs a nuclear spindle arises in a similar way 
and the chromatin assumes the form of a spireme preparatory to 
breaking up into chromosomes, but, instead of 36, only 18 of these 
latter bodies appear. The subsequent changes are identical in both 
kinds of eggs. The chromosomes split longitudinally and each half 
moves along the spindle fibres toward its respective pole. As they 
approach the poles the chromosomes swell up and eventually fuse 
together to form a single nucleus in the region occupied by each of the 
diffuse centrosomes. Meanwhile a cell wall develops between the two 
nuclei dividing the cytoplasm into two, and finally the spindle fibres 
disappear. The succeeding processes of development, both internal 
and external, are similar in both naturally and chemically fertilized 
eggs, with the exception that at each succeeding division only 18 chro- 
mosomes appear in the latter instead of the normal number, 36.1 
We had mentioned that the eggs which formed a membrane 
upon butyric-acid treatment begin to divide and may go through 
a series of divisions if the temperature is sufficiently low. 
According to Hindle, at room temperature only a monaster is 
formed with the nucleus as a center, while at a low temperature 
a typical amphiaster is formed. The subsequent changes in the 
latter case are the same as with the treatment with hypertonic 
sea-water. 
1 Hindle, op. citi. 
