MUSEUM OF COMPARATIVE ZOOLOGY. 297 



of the nuclear " substance " which is accumulated at the poles of the elon- 

 gated nucleus exerts an attractive influence on the surrounding proto- 

 plasm, it seems only natural to inquire why the greater mass, accumulated 

 at the equator, does not exercise a like influence, and why it is that the 

 latter seems to respond quite as passively as the protoplasm to the at- 

 tractive influence of the centres of the asters. I am inclined to think 

 that the astral phenomena are not to be explained so simply as by the 

 assumption that they are due to the attractive influence of a segregated 

 portion of the nuclear " substance " as such ; but that it is more likely 

 they arise in response to a force set free by rapid chemical changes at 

 definite points in the protoplasm. From the usual proximity of those 

 points to the nuclear structure, it seems highly probable that the chemi- 

 cal changes are sustained by the direct mingling of the substance of the 

 nucleus with the protoplasm ; there are some cases, however, (e. g. 

 Limax,) where the evidence of a direct mingling is wanting, — where 

 the early participation of the substance of the nucleus may possibly be 

 called in question. 



Hertwig maintains the morphological integrity of the nucleus through- 

 out the metamorphosis. If such is the case, are we not justified in ex- 

 pecting that its attractive influence will continue to be exerted from the 

 beginning to the end of the process? In that event, the two asters 

 which arise with the lengthening and polar differentiation of the nucleus 

 ought to be genetically connected with the single aster which first radi- 

 ates from the " Furchungskern." Selenka, it is true, has recently main- 

 tained this very position, but I believe that Hertwig (p. 416) is right 

 when he practically denies the existence of a genetic connection in saying : 

 " Dann lost sich die alte Radienfigur allmalig auf und es entstehen zwei 

 7ieue an den beiden Polen des Kerns. Dieselben sind anfangs klein, 

 u. s. w." Hertwig believes the amphiaster becomes explainable as the 

 result of the attractive influence of the nucleus on the protoplasm, as 

 soon as we assume that with the lengthening of the nucleus there is a 

 distribution of the forces of attraction to its poles.* I find nothing to 

 support this conclusion, since I see no evidence of a genetic connection 

 between the single and the double asters. Both may be the result of 

 like chemical changes, but certainly the latter are not referable to the 

 direct attraction of the nucleus, or a segregated portion of it. 



* " Auch diese Erscheinungen erklaren sich aus einer Anziehung, welche der Kern 

 auf das Protoplasma ausiibt, wenn wir annehmen, dass die zu Aiifang in der Kern- 

 kiigel nach alien Eichtungen gleichmassig wirkenden Anziehungskrafte bei der 

 Streckung des Kerns auf die zwei Pole desselben sich vertheilen." 



