490 ROBERT CHAMBERS, JR. 



II. EXPERIMENTAL 



1. The Aster 



The fully formed aster (cf. one of the asters in the illustration 

 t)f the amphiaster in figure 10) in the Echinarachnius egg^ 

 consists of a central, hyaline, more or less spherical area, the 

 sphere, from which radiate an enormous number of narrow rays 

 consisting apparently of the same hyaline substance as that of the 

 sphere. The rays are broadest at their base and gradually taper 

 along their course to lose their identity before quite reaching the 

 margin of the cell. The cell nucleus lies in the sphere somewhat 

 to one side of the center (fig. 7). The granular cytoplasm sur- 

 rounds the hyaline rays and projects between them into the 

 sphere in the form of shorter or longer conical processes (fig. 1). 

 The sphere consists of a clear non-viscous liquid. The needle 

 may be moved about in it without a disturbance of the surround- 

 ings. Before the nucleus has increased much in size, it may be 

 pushed about with ease in this liquid area. On the other hand, 

 the cone-like projections of cytoplasm are very solid in compari- 

 son. They may be bent (fig. 2) and pulled about and act as . 

 comparatively rigid gelatinous structures with the cytoplasmic 

 granules immovably embedded m them. The rays consist of a 

 liquid similar in appearance and consistency to that of the sphere. 

 The cytoplasm through which the rays extend is solid when 

 ■contrasted with the liquid cytoplasm of resting eggs. In short, 

 dissection of a cell containing a fully developed aster gives one 

 the impression that the cytoplasm is in the gel state, while the 

 sphere and its rays are liquid. 



The gel state is most pronounced in the cytoplasm bordering 

 the sphere, its rigidity diminishing as one approaches the periph- 

 ery of the cell. The comparative stabihty of this gel state 

 allows of considerable distortion without a destruction of the 

 aster. At the height of the astral stage the aster may be twisted 

 into a spiral or other distorted shapes. On remo\dng the needle 



' The aster in Cerebratulus, Arlmcia and Asterias agrees essentially with 

 the above description. 



