MUSEUM OF COMPARATIVE ZOOLOGY. 579 



envelope becomes visible. This pseudo-membrane surrounds only the middle 

 part of the nucleus ; it is wanting at the ends. The grain at the middle 

 of each filament is evidently a simple enlargement of its substance. The 

 unipolar rays are extremely delicate toward their extremities, and at one 

 point are much swollen. Unlike those of the interior of the nucleus, — which 

 are more rounded, distinct, and refringent, and perfectly regular in their 

 arrangement, — these enlargements are elongated, variable in form, and placed 

 at irregular distances from the centre of the aster, so that the enlargements of 

 consecutive filanients never lie adjacent to each other. There may be filaments 

 with two enlargements, others with none. The effect of staining in gold 

 chloride appears to be, to a certain extent, an indication that the view I have 

 expressed about the nature of the spindle fibres at their initiation is erroneous. 

 Fol observes with this treatment that the asters assume a beautiful dark violet 

 color, which at the periphery gradually merges into the color of the yolk, which 

 is of a rose tint. The nucleus and the intranuclear rays, without being de- 

 stroyed, remain pale, — " are not more stained than the rest of the vitellus." 



The next phase is characterized by the division of the fibre thickenings, 

 which cannot be observed, however, in the living egg. The vitellus changes 

 form, now in one direction, now in another, but ultimately elongates in the 

 direction of the axis of the amphiaster. In picric acid the enlargements, after 

 division, appear larger and more elongated than in the preceding stage. The 

 interzonal filaments are very pale, and soon disappear ; they are named " fila- 

 ments connectifs." The flattening of the amphiaster increases, so that the 

 spindle and areas appear in one position twice as broad as they do after being 

 rotated 90° about the axis of the spindle. The granules of the " area " (sarco- 

 dic mass) are also extended in the same plane in the form of a cylindrical bol- 

 ster, which may be straight or slightly curved. The extranuclear rays form a 

 compact zone around the "area," and ap'pear composed of pieces in juxtaposi- 

 tion like the bricks in an arch. Toward the exterior these pieces are continuous 

 with granular rays. This structure is of limited extent, and since it exists at 

 precisely the time when the rays in the living egg extend to the periphery of 

 the yolk, it is to be concluded that the rays consist of two distinct parts, of 

 which one (the central) is brought out by picric acid, while the other (pe- 

 ripheral) is only seen in living eggs. The author cites two figures (PI. VII. 

 Figs. 9, 11) to illustrate the condition shown at this stage after treatment with 

 acetic acid. The description relates principally to Fig. 11. The nuclear fila- 

 ments are not distinguishable from those of the vitellus, and the granular 

 mass at the centre of the aster, not being discernible, is probably veiled by 

 them ; but the region which extends between the two groups of intranuclear 

 enlargements * is not thus covered ; one should therefore be able to see the 

 filaments which connect these enlargements in pairs, f if they exist. It is easy, 



* In Fig. 1 1 no such groups are represented, mdess, as the author may possibly 

 have assumed, they are already fused with the "sarcodic mass" at the astral centres. 



t Fig. 9 shows a spindle with equatorial enlargements ; consequently the " con- 

 nective filanients " are not to be sought in that stage. 



