No. I.] THE ECHINODERM EGG. 325 



ance the amphiaster (Fig. 3, D) corresponds closely with Fol's 

 jfigure, the center of each aster being occupied by a clear 

 sharply circumscribed archoplasm-sphere {^' astrosphhe'' of 

 Fol). This sphere is described by Fol as consisting of a clear 

 liquid or jelly in which is suspended a single centrosome 

 (" astrocentre "), the latter having arisen through the fusion of 

 the paternal and maternal " demi-centers." This description 

 is totally inapplicable in the case of Toxopneustes. The central 

 sphere here consists of a distinct reticulum with thickened 

 nodes, staining bright red after iron-haematoxylin and Congo 

 red or acid fuchsin, while the astral rays are blue. The ap- 

 pearance of the reticulum varies somewhat according to the 

 mode of fixation. After Flemming's fluid the fibres are ex- 

 tremely distinct but very delicate. After sublimate or chromic 

 acid the nodes are much coarser and the fibres less distinct. 

 Sublimate-acetic (the best reagent for the archoplasmic struc- 

 tures in general) gives an effect intermediate between the two 

 foregoing methods. Picro-osmic has a very destructive action, 

 the reticular substance being disorganized and broken up into 

 clotted granules, often leaving the " astrosphere " quite empty, 

 or containing one or more irregular clumps closely similar to 

 those described by Fol as " centrosomes." In Toxopneustes 

 these are unquestionably artefacts — mere fortuitous groups of 

 granules, inconstant both in number and size. In well-pre- 

 served material the thickened nodes of the reticulum appear as 

 granules (clearly shown as such in photographs) uniformly dis- 

 tributed through the astrosphere, and there is absolutely noth- 

 ing to be identified as a centrosome. 



During the anaphase the central sphere rapidly increases in 

 size and becomes much looser in texture (Fig. 4, A), and as 

 the daughter-nuclei are reconstituted the astral rays become 

 less distinct, the aster finally appearing as a large blue granular 

 mass almost amoeboid in outline and traversed by faint rays. 

 The nucleus is withdrawn into the interior of this mass and is 

 pressed against the red reticular mass, which flattens down 

 upon it like a cap (Fig. 4, B) and in some preparations seems 

 nearly to surround the nucleus. The egg meanwhile divides 

 into two. The central archoplasm-mass now divides (in a plane 



