494 ROBERT CHAMBERS, JR. 



acquires a squatty bipyramidal shape with its broad equator 

 spreading quite across the sphere. The sphere then takes on the 

 shape of two semilunar areas lying over the two poles of the 

 nucleus (fig, 9). The rays soon blaze out again but this time 

 around two centers, the two polar areas, producing a brilliant 

 amphiaster (fig. 10). The rays extend almost to the periphery 

 of the egg and with the needle it is possible to show that the 

 cytoplasm is again a comparatively rigid gel. 



As the astral formation extends into the equator of the amphi- 

 aster the gelled strands of the two asters become irregular and 

 distorted in shape where strands from opposite directions meet 

 (fig. 10). The gelation figure here is a meshwork of strands 

 rather than Hnear strands such as form between the rays else- 

 where. In the immediate vicinity of the nucleus, however, the 

 strands form continuous lines and since many lie directly on the 

 nucleus, give it a fibrous appearance. No fibers of any kind 

 could be distinguished within the substance of the nuclear 

 spindle. 



Soon after the amphiaster has fully formed the bipyramidal 

 nucleus lengthens into a long oval body (fig. 10). Its bulging 

 equator gradually retracts until its sides are fairly parallel. At 

 this stage in Toxopneustes (Wilson and Mathews, '95) Wilson 

 describes a pause of some duration during which the astral 

 radiations become very much reduced in extent. In Echina- 

 rachnius the asters and the cytoplasm remain in the gel state 

 although the rays appear to be less brilliant than hitherto. 

 After a space of time (about ten minutes) a change takes place 

 in the cytoplasm about the equator of the nuclear body which 

 appears to be a reversal to the sol state. I was not able to con- 

 vince myself on this point by the use of the needle. The cyto- 

 plasmic granules, however, which were hitherto held in a gel, 

 become visibly mobile in the equatorial region where the rays 

 of the two asters meet. As a constriction in the equator of the 

 nuclear body deepens and widens a distinct flow of the granules 

 medianward can be observed, that is, into the region of the con- 

 striction (fig. 11). Following this a constriction in the equator 

 of the cell takes place and one gains the impression that this is 



