MUSEUM OF COMPARATIVE ZOOLOGY. 527 



conceive what influence the mutual relation of the pronuclei could have 

 in determining the place of the two stars. From my observations on 

 Limax I am of the opinion that the pronuclei exercise only a limited in- 

 fluence on the position of the first amphiaster. As the centres of its 

 stars may lie deeper in the yolk* (farther from the animal pole) than the 

 pronuclei, I am induced to think that their positions are determined 

 by some unl^nown influence which probably resides in the protoplasm 

 itself, and in this I see another reason for hesitating to consider the 

 asters as the result of an attraction exerted by a part of the nuclear 

 body on surrounding protoplasm. 



The theory that the stellate figures are due to the outstreaming of 

 nuclear fluid from the nucleus undergoing division or disintegration, 

 leaves the existence of male asters without an explanation, for there is 

 no pre-existing accumulation of nuclear fluid to be thus put in motion. 

 Even as applied to the nucleus undergoing division, it is confronted by 

 serious obstacles, some of which I have already (p. 286) stated. As with 

 every other theory which involves a circulation of fluid, the results ap- 

 pear disproportionate to the protracted period during which the supposed 

 "flow " is maintained. There is no accumulation of the clear (nuclear'?) 

 fluid at the peripheral ends of the rays such as might be expected to re- 

 sult from so long continued a current, and when the rays ultimately dis- 

 appear it is first at their peripheral ends, — not at their central ends, as 

 would naturally result if there were an outflowing stream. Apparently 

 the only way of explaining this method of disappearance, in keeping with 

 the theory of centrifugal currents, is by assuming that the nuclear fluid 

 in the rays becomes diffused through the yolk, and that this diffusion 

 begins, or proceeds more rapidly, at the distal ends of the rays, thus 

 inducing their earlier obliteration near the periphery. But, if that were 

 possible, might not the original distribution, as readily as this, have 

 ta^ken place as a uniform diffusion through the whole yolk without en- 

 gendering any astral figure 1 Certainly the rapidity with which the stars 

 grow is not so much greater than that of their disappearance as to make 

 it possible for simple diffusion to accomplish one, and not the other. It 

 is also incredible that fluid forced from the tips of an elongate nucleus at 

 so slow a rate as must be conceded, should exhibit such fineness and 

 such marvellous uniformity in the nature and the direction of its cur- 

 rents, unless some pre-existing structural condition determined its 

 course. 



But the principal objections to this view, which was first advocated by 



* See Figs. 85-89, 



