232 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
are both closer together and larger (pi. 15, fig. 37). Furthermore, 
the relative positions of the nuclei in figure 22 (plate 13) cannot be 
explained on such an assumption. 
If, then, these are incipient stages of fertilization, as the facts cer¬ 
tainly suggest, what force or forces cause this peculiar shape ? It is 
clear that there are only three possible agencies that could bring the 
sexual nuclei together: an amoeboid movement of the nuclei them- 
selves; or, the sperm nucleus could be forced in by greater hydro¬ 
static pressure in the antheridium at the time the perforation is 
made; or finally, they might be strongly attracted into a common 
region of the egg. There is nothing to suggest an amoeboid move¬ 
ment and little to indicate the second of these agencies unless it is 
that the antheridium becomes extremely dense just before it opens 
and the additional fact that the sperm nucleus often changes its 
course after it enters the central ooplasm. If the sperm nucleus 
were forced in, however, it should, in passing into the dense central 
portion, flatten on its anterior surface. On the contrary, the advanc¬ 
ing nuclei are elongated in the direction of migration suggesting 
that they are moving in response to a strong attraction. It is possi¬ 
ble that the pointing is accentuated by the fact that the intervening 
substance is extremely compact and the bodies in moving through it 
meet with considerable resistance. Throughout the investigation 
the evidence has suggested that the entire nuclear movement is a 
response to two forces: one acting first, that brings the nuclei into 
the interior of the egg; and another, manifesting itself later, that 
draws the nuclei together. Such an assumption would seem to 
explain the change of course that the sperm nucleus so often makes 
after it enters the central portion of the egg. 
In almost all cases this change of course as well as the formation 
of the nuclear beaks can be accounted for on the ground of strong 
mutual nuclear attraction. It is entirely probable, furthermore, 
that the peculiar form of the nuclei is an expression of the action .of 
this force. There are some instances, however, that are difficult to 
account for on such aground. In figure 22a (plate 13) for example, 
the sexual nuclei put out beaks that form an angle of less than 70° 
and in figure 18b (plate 13) the beaks also form a sharp angle. It 
may be noted, furthermore, that the beaks in these cases and in all 
others as well, are burned approximately toward the center of the 
differentiated ooplasm. This would indicate that its center really is 
