PLATE XXXI 1. 



Fig. 1. Ctenolabrus [Tautngolabrus adspersus (Walbaum)] [early 16-c'cll stage viewed] from below 



(12) (within), [be = blastocoele or cleavage-cavity], Osmic and Merkel. Cap of cells browned, 

 pellicle stained lightly red. Vacuoles occur along all of the cleavage-lines except 4-4. 4'-4\ in 

 which the cleavage is not completed. Along the line 3-S, especially in the breakage lines of 

 1-1, 3-3. S'-3', the vacuoles form the roof of the cleavage-cavity and are seen to be uncolored, 

 giving the appearance as if the cavity opens above as well as below. But [this is not the case 

 since] there is a line of division running between the vacuoles always. These vacuoles are all 

 on the outer surface of the lines (not on the under side) . Very few are seen elsewhere in the 

 cells. The astral arrangement of protoplasm around nuclei is strong, especially in the two 

 pairs of end-cells, which are here plainly larger than the median cells. 



The outlines of the middle cells are sharp against the pellicle, of the end-cells obliterated very 

 strongly in region of cleavage-planes (4-4. 4'-4')- 



In the corner-cells of the right half of figure we see that, on the upper surface, they abut 

 against the nearest median cell of opposite side. The upper left corner-cell is nearer to the 

 median of opposite side on the under surface than on the dorsal. This is the only case where 

 conditions similar to those in a frog occur. 



Notice that the lines of the corner-cells have a tendency to take a radial direction, in harmony 

 with the position of their nuclei. 



The cleavage-cavity now cover.'^ a little more than the four central daughter cells, the angles 

 being prolonged in the cleavage-lines, sometimes nearly or quite to the periphery. Along line 

 2-2 the cavity deepens rapidly by sloping sides to the line of vacuoles which form the roof. 

 This cleavage-cavity is found in all eggs of this stage. Only four distinct lenticular spaces seen 

 (dotted in Fig). Lowering the focus a little we see that the longest ends of the rectangular area 

 dip down beneath the surface, one turning to the right, the other to the left. Just beyond the 

 longest angles are seen two lenticular areas such as are often seen in fresh specimens; these 

 appear to be in the surface. The nuelei are also near the surface (upper surface Fig.). 



This preparation is from Merkel's fluid, and hence the whole cap is colored dark red, the 

 pellicle being only faintly stained. 



Numerous small vacuolar spaces are seen in the spheres, as well as in the pellicle. I do not 



know if due to reagents. These vacuoles are found in all preparations of the caps. 



Fig. 2. Ctenolabrus; 16-cell stage from below. Osm. \% 20 m. Merkel. Shows every nucleus 



(18) in state of division, eight lenticular spaces, the outer boundary of cleavage-cavity (6c) and the 



boundary-lines with vacuoles on the upper surface of cap. The line of junction between the 



two central cells (a.b) is about twice as long on the under as the upper side. 



Notice that the general trend of all the nuclei, except two at hind end, is at right angles to the 

 first cleavage-plane. We have here a difference between fore and hind end. The outline of 

 the cap is very sharp everywhere, but the cap is rounded at the margin, so that the pellicle 

 does not join the sharp edge, but does so at a lower level, i. e. near the lower (inner) surface of 

 cap. [Cf. Plate xxxv, fig. 1, 8th section, top end]. 



The nuclear figures of four central cells appear shortened because they do not lie horizontally. 

 It is the inner end of these spindles that lie lower (nearer the internal side) than the outer poles. 



The twelve marginal cells are stained darker than the four central cells — giving the ring 

 seen in colored drawing. 



The achromatic poles of nuclear figures are here quite distinct, they are often convex on the 

 outer side and concave on the inner sides. 



