MUSEUM OF COMPARATIVE ZOOLOGY. 589 



(Flemmmg's) it is to be seen that the polar globule is half formed at this time, 

 and consequently " Biitschli's corpuscles " are already divided. As is known, 

 the external aster is incomplete, its centre having arrived at the surface and 

 being only partly surrounded by unipolar filaments. It is therefore natural to 

 presume, he says, that the pseudopods correspond to unipolar filaments, which 

 are wanting in consequence of the superficial position of the aster. If this rea- 

 soning is correct, he adds, this is a case where the filaments are elongated in a 

 centrifugal direction during a part of the period of division, to be subsequently 

 retracted. If the pseudopodia belonged to a somewhat earlier phase, I should 

 think there would be greater justice in this conclusion. The position of the 

 rays after the division of the equatorial zone, as shown in Limax, Fig. 50, does 

 not seem easily reconcilable with Fol's interpretation. 



But the observations of Strasburger on Spyrogyra also tend, continues the 

 author, to establish the existence of centrifugal currents during the division 

 of the amphiaster. If, now, we compare the unipolar filaments with these 

 pseudopodal filaments (Spirogyra), the former should be considered as streaks 

 of sarcode stretching out toward the periphery, but having the opposite course 

 after the division of the intranuclear enlargements. 



The changes within the nucleus are also instructive. The formation of the 

 spindle from the intranuclear network and the division and migration of the 

 fibre thickenings appear to result from an action exercised upon the interior of 

 the nucleus by two centres placed at its poles. It is not possible to say what 

 the nature of this action is. An internal repulsion would not explain the 

 eccentric position of the " amphiaster de rebut." A simple attraction would 

 not explain the formation of Biitschli's corpuscles. On the other hand, the last 

 part of the act of division, the formation of new nuclei, appears explainable 

 upon the hypothesis of an attraction exerted by the centres upon their vici- 

 nage, and of the mutual repulsion of the asters. A central attractive influence 

 on the part of the new nuclei would explain the process of segmentation, ex- 

 cejDt in the case of the polar globules. 



The evidences of the existence of repulsions are the progressive separation of 

 the poles of the amphiaster and the mutual repulsion of the male asters. After 

 the female pronucleus has been superfecundated the conjugated nucleus and the 

 independent male asters are all situated at the external third of vitelline mjs. 

 This regularity of situation indicates that they occupy a position of equilibrium 

 between opposing forces, and these forces can only be an attraction toward 

 the centre of the yolk on the one hand, and a mutual repulsion on the other. 

 The attraction between the sexual nuclei is a special case in which this force 

 is very evident. The motion of the male aster is correlated with the position 

 of the female pronucleus ; it has not a constant relation with the vitellus. 



In the further development, the ifiale elements exercise a preponderating 

 influence, as the existence of the tetraster after fusion with more than one 

 zodsperm shows ; the isolated male asters pass through the stages of amphi- 

 astral division, but the isolated (unfecundated) female pronucleus decomposes 

 without exhibiting any of these changes. 



