CELL DIVISION IN EGGS OF CREPIDULA. 589 



r 



PLATE LV. 



Effects of Hypertonic Sea Water. 

 All eggs shown on this plate are from Exp. 804, and were subjected to 1 per cent. NaCl in sea wate 



Figs. 159-163. The sperm nucleus lies in a small area of cytoplasm near the lower pole; the egg 

 leus lies in a larger area of cytoplasm at the animal pole; various stages in the formation of the egg spindle 



Fig. 164. Two spindles, probably those of egg and sperm, are joined at one pole. 

 Figs 165 166. Tetrasters, probably formed from the egg and the sperm spindles. 

 Fig. 167. ' Two spindles, probably those of the egg and the sperm, joined at one pole. 

 Fig! 168! Two spindles, probably those of the egg and sperm, quite separate. 

 Figs. 169 170. Tetrasters in different phases of the separation of the chromosomes. 



and 



PLATE LVI. 



Effects of Hypertonic Sea Water. 



71. Exp. 823: 3 per cent. NaCl, 16 hrs., normal 8 hrs. Egg nucleus very small and clear with 

 les persistent within vesicle and egg centrosome outside vesicle; the sperm nucleus is enormous 

 ns much chromatic sap. 



* „. .72. Exp. 823: Similar to the preceding. ; 



Fig. 173. Exp. 837: 1 per cent. KC1, 9 hrs., normal 35 hrs. Development has been stopped but the 

 rg is not dead; the germ nuclei are very large and achromatic; small achromatic spherules lie in the cyto- 



Fig. 174. Exp. 822: 2 per cent. NaCl, 16 hrs., normal 8 hrs. Achromatin in large and small vesicles 



I the cytoplasm; germ nuclei normal. ■"'■-. . , . , , - A , , 



.75. Exp. 822: The germ nuclei are broken up into many separate vesicles, each with a chromatic 



nucleolus. 



achromatic. 



Exp. 823: Two-cell stage from same experiment as figs. 171, 172; nuclei very large and 

 Exp. 822: Side view of egg in 2-cell stage, each cell containing a large sphere (S) and one 



or more chromatic and two or three achromatic . 



Fig. 178, 179. Exp. 810: 3 per cent. NaCl, 15 hrs.: Side views of egg in 2-cell stage showing 

 chromatin massed within the nuclear vesicle ; the latter are elongated along the line of the former spi 



axis. ...... . , 



Figs. 180-182. Same experiment 



Fig. 180. In one half of egg the i 



and 



formed 



sph 



'Fig. 181. Nuclear vesicles elongated along the spindle axis are present in three of the cells, and in 

 each the chromatin is massed at the end of the vesicle nearest the sphere; in the fourth cell no nuclear vesicle 



is present, but traces of spindle fibres may be seen. t . .. .. M 



Fig. 182. In all four cells the nuclear vesicles are rounded and the chromatin is massed near the center 



of each vesicle. 



PLATE LVII. 



Effects of Hypertonic Sea Water. 



Figs. 183-185 were in 1-cell stage at beginning of experiment; Figs. 186-196 were in 2-cell stage. 

 Fig. 183. Exp. 805 : 2 per cent. NaCl, 4 hrs. ; in both egg and sperm nuclei the chromatin is aggregated 

 into a dense mass in the center of the nuclear vesicle; there are many cytasters near the sperm nucleus. 

 Fig. 184. Exp. 809: 2 per cent. NaCl, 15 hrs.; the chromatic and achromatic parts of the germ 



nuclei are in separate vesicles. . ,, . „ 



Fig. 185. Exp. 809: Similar to the preceding; a double cytaster is present near the germ nucleus 

 Fig. 186. Exp. 809: 2 per cent. NaCl, 15 hrs.; the chromatic and achromatic parts of the nucleus are 



in separate vesicles ; the achromatic vesicles are numerous and scattered. 



Fig. 187. Exp. 809 : Side view of egg similar to preceding. ..... #._i% 



Fig. 188. Exp. 809: Egg similar to the preceding showing two principal achromatic vesicles (Acn) 



and many smaller vesicles or sphere granules. . ., _ . .„,_!,.. : n 



Figs. 189, 190. Exp. 805: 2 pe? cent. NaCl, 4 hrs.; the 2d cleavage Bundles are much «hnmken m 

 size; the archiplasm around them is much condensed while many small radiating masses of archipiasm 

 are left along the astral radiations as cytasters. , ... . _ » „„_ ci,-^™ 



. Figs. 191, 192. Exp. 823: 3 per cent. NaCl, 16 hrs., normal 8 hrs.; top and side views ^Wj 

 in addition to the principal masses of chromatin (Ch) very numerous granules or spherules which prooaoiy 



represent scattered achromatic material (Ach). . _ mmmm y. ar .. TnTn0r ^ haw 



Figs. 193, 194. Exp. 837: 1 per cent. KC1, 9 hrs., normal 36 hrs.; the numerous karyomeres have 



begun to absorb achromatin and to fuse together. 



