1892.] Heredity and the Germ- Cells. 647 
stant in all the cells of the same variety through all stages; 
thus the same number of chromasomes appears in the first 
segmentation of the fertilized ovum as in the subsequent cell 
division in the tissues. 
Carnoy next indicates the vertical splitting of each rod into 
a loop or link preceding the horizontal splitting; thus we may 
conceive of a thorough redistribution of the chromatin before 
it passes into the daughter-cells. The split loops are each 
retracted toward a centrosome, suggesting to some authors a 
contractile power in the archoplasmic filaments; each chro- 
masome being apparently withdrawn by a single filament. 
But as the chromasomes separate, the filaments also appear 
between them, and are variously termed “interzonal,” “ ver- 
bindungs Fäden,” “ filaments réunissant;” there is, therefore, 
some difference of opinion as to what the mechanics of the 
chromasome divisions really are. The chromatin is now 
retracted into two coiled threads, each the centre of tie daugh- 
ter-nucleus with asingle centrosome beside it. But as the line 
of cleavage is drawn between the two cells (fig. 9), the single 
centrosome in each cell divides so that each daughter-cell is 
now complete with its chromatin coil and two archoplasmic 
centrosomes. This process has been beautifully described by 
Watase.” 
It thus appears that both the chromatin and archoplasm 
are permanent elements of the cell, such as we formerly con- 
sidered the nucleus; the apparently passive chromatin is 
divided with great precision by the active archoplasm, then 
the archoplasm simply splits in two to resume the cleavage 
function. 
Fertilization—The Union of Hereditary Substances.— 
Before looking at the host of questions which fertilization sug- 
gests, let us review a few of the well-known phenomena pre- 
paratory to the union of the germ-cells, in order to give greater 
emphasis to the importance of recent discoveries. 
First, the ovum is a single cell, the typical structure of 
which, with its nucleus and cytoplasm, is generally obscured 
*See Marine Biological Laboratory Lectures, 1889. Boston: Ginn & Co. 
