MUSEUM OF COMPARATIVE ZOOLOGY. 569 



female pronucleus. On another point our conclusions are less in agreement. 

 Fol says the half of the amphiaster remaining in the vitellus contracts and 

 passes through a short period of repose. Its arrangement remains the same as 

 during the formation of the first polar globule, but it momentarily fades a 

 little. It becomes more distinct when the work of expulsion recommences ; 

 the bipolar filaments elongate, the aster becomes larger, more marked, and far- 

 ther removed from the surface. The elongated bipolar filaments form again a 

 fusiform body, the interior extremity of which corresponds to the centre of 

 the aster, while the exterior extremity is found at the surface of the vitellus. 

 This external point of convergence is not yet surrounded with rays ; but uni- 

 polar rays soon appear around it, so that exactly the same figure is produced as 

 at the formation of the first polar globule. The exterior aster of the second 

 amphiaster almost always lies at one side of the point of contact of the vitellus 

 with the first globule, and the axis of the amphiaster is usually oblique. His 

 positive assertions that the internal half of the amphiaster is not massed into 

 a nucleus, but is transformed directly into a new amphiaster, makes me some- 

 what distrustful of the conclusions I have expressed on this point; it is at 

 least of some significance that the granulations at the internal ends of the 

 spindles in my Figs. 22, 25, 40, are less conspicuous than the corresponding 

 thickenings in the polar globules. I, however, still believe this feature deserv- 

 ing of renewed investigation. Fol believes the peculiar position of the centre 

 of the external aster at the apex of the elevation is explained by the nature of 

 its physiological rdle expressed in the name, spherules de rebut. 



I can confirm for Limax (Fig. 80") what the author thinks probable in As- 

 terias, namely, that the envelope of the polar globule is continuous with that 

 of the vitellus, rather than that the latter is pierced by the forming globule, 

 although I have not found the envelope especially thin at the summit of the 

 polar cell (Figs. 22, 25, 40, 61-63). 



During the constriction of the peduncle of the polar globule in Asterias, Fol 

 has observed, as did 0. Hertwig, the existence of folds in the vitelline envelope, 

 radiating from the peduncle on all sides, and most prominent near its base. 

 This he believes indicates the presence of a superficial layer more inert, less 

 living than the protoplasm which it surrounds, but not the existence of a veri- 

 table membrane ; a membrane, however elastic it may be, finally becomes 

 detached from the yolk, and assumes its former position. This it does instantly 

 under the influence of acids. But here the so-called membrane follows the 

 division of the protoplasm, and forms an envelope around each of the segments, 

 never resuming its former position, even if one employs acids before the di- 

 vision is efi'ected. The same conclusions appear equally applicable to Limax, 

 although in some cases (Fig. 80°) it may be difficult to assert that the envelope 

 has not reached a degree of diff'erentiation which closely approaches that of a 

 genuine membrane. I have only once seen anything like radiating folds at the 

 surface of the segments, and then (Fig. 68) they were confined to the polar 

 globule. 



Of the formation of the female pronucleus in Asterias, the author says that 



