590 CELL DIVISION IN EGGS OF CREPIDULA. 



Figs. 195, 196. Exp. 808: 1 per cent. NaCl, 15 hrs.; top and side views of eggs with two macromeres 

 and two micromeres, each with many masses of chromatin (karyomeres) and several spheres or asters. 



PLATE LVIII. 

 Effects of Hypertonic Sea Wateb. 



All eggs represented on this plate were put into hypertonic solutions in the 1-cell stage, and with the 

 exception of fig. 197 none of them show division of the yolk. 



Fig. 197. Exp. 842: 4 per cent. MgCl», 5 hrs., normal 17 hrs.; the two cells at the upper pole are 

 probably enormous polar bodies, both of which contain mitotic figures. 



Fig. 198. Exp. 991: 1 per cent. MgCl 2 , 18 hrs.; one large cell (macromere) contains all the yolk, two 

 smaller cells (micromeres) are purely protoplasmic; both macromeres and micromeres contain many nuclei 

 (karyomeres), the chromatin of each being condensed into one or two masses. 



Fig. 199. Exp. 834: 3 per cent. MgCl 2 , 9 hrs., normal 9 hrs.; both macromere and micromere contain 

 mitotic figures with many poles and scattered chromosomes; sphere granules at the animal pole of the 

 micromere. 



Fig. 200. Exp. 833: 2 per cent. MgCI 2 , 9 hrs., normal 9 hrs.; resting stage following a division stage 

 like that of the preceding figure. 



Fig. 201. Exp. 838: Herbst's Ca-free sea water, 18 hrs.; micromere and macromere containing 

 many nuclei and cytasters. 



Fig. 202. Exp. 825: 2 per cent. NaCl, 16 hrs., normal 23 hrs.; two spheres and many scattered nuclei 

 (karyomeres) in both macromere and micromere. 



Fig. 203. Exp. 827: § per cent. NaCl, 9 hrs., normal 8 hrs. ; many asters and scattered chromosomes 

 in the macromere and in one of the micromeres. 



Fig. 204. Exp. 863: 2 per cent. NaCl, 2J hrs., normal 10 hrs.; similar to the preceding; scattered 

 spindles and chromosomes; three small micromeres (lobes) budding off from the macromere; sphere granules 

 at the animal pole of the micromeres. 



Fig. 205. Exp. 843: 1 per cent. NaCl, 6 hrs., normal 15 hrs.; several micromeres, three of them 

 containing several nuclei or groups of chromosomes; the macromere contains many nuclei (karyomeres). 



Fig. 206. Exp. 827: f per cent. NaCl, 9 hrs., normal 8 hrs.; macromere and micromeres containing 

 many karyomeres and asters. 



Fig. 207. Exp. 830: 2 per cent. NaCl, 9 hrs., normal 32 hrs.; macromeres and micromeres containing 

 a large number of karyomeres or asters; sphere granules under the polar body. 



Fig. 208. Exp. 833: 2 per cent. MgCl2, 9 hrs., normal 9 hrs.; many nuclei (karyomeres) and spheres 

 in each cell. 



PLATE LIX. 

 Effects of Hypertonic Sea Water. 



Eggs represented in figs. 209-218 were in the 2-cell stage when the experiments began, and in none of 

 them did the yolk undergo any subsequent cleavage; figs. 219-223 were in the 4-cell stage at the beginning 

 of the experiment. 



Fig. 209. Exp. 865: 4 per cent. NaCl, 2 hrs., normal 10 hrs.; the nuclear division at the 2d cleavage 

 occurred regularly but the cell division was suppressed, thus leaving two nuclei of normal appearance, in 

 each cell; at least three spheres are present in the left cell. 



Fig. 210. Exp. 804: 1 per cent. NaCl, 4 hrs.; partial suppression of the 2d cleavage furrow which is 

 limited to a shallow furrow on the animal pole side of the egg; the nuclei are irregular and densely chromatic. 



Fig. 211. Exp. 864: 3 per cent. NaCl, 3 hrs., normal 10 hrs.; the 2d cleavage spindles have the position 

 of the 3d cleavage spindles of normal eggs; the chromosomes are scattered abnormally on the spindles. 



Fig. 212. Exp. 865: 4 per cent. NaCl, 2 hrs., normal 10 hrs.; the two macromeres have each given 

 off a first and a second micromere, the first by dexiotropic and the second by Inotropic division, as in normal 

 eggs. Each of the first micromeres contain a single nucleus and sphere; the second micromeres and the 

 macromeres contain several spheres and karyomeres or groups of chromosomes. 



Fig. 213. Exp. 863: 2 per cent. NaCl, 2 J hrs., normal 10 hrs.; the first set of micromeres have been 

 formed in dexiotropic direction, as in normal cleavage; the macromeres are dividing again with double 

 spindles or tetrasters. 



Fig. 214. Exp. 846: 4 per cent. MgCl 2 , 4 hrs., normal 16 hrs.; the two macromeres are separated by a 

 group of micromeres which have formed along both sides of the 1st cleavage plane; the polarity of each half 

 thus appears to have been changed, the centers of the ectodermal pole being the surface of contact between 

 the two halves; this may be due, in part, to the outward rotation of the macromeres at the vegetal pole 

 and their inward rotation at the animal pole. 



Fig. 215. Exp. 846: 4 per cent. MgCl 2 , 4 hrs., normal 16 hrs.; side view of an egg with two macro- 

 meres and six micromeres; the two original micromeres of the first set have subdivided as indicated by the 

 arrows, the other two micromeres are of the 2d set; all the micromeres contain karyomeres; the macro- 

 meres contain chromosomes scattered apparently, along the line of the 1st cleavage spindle. 



