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 macromen* 



micromeres 



astert 



PLATE LVIII. 



Effects of Hypertonic Sea Water. 



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 2 , 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. MgCl 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: f per cent. NaCl, 9 hrs., normal 8 hrs.; many asters and scattered chromosomal 

 in the macromere and in one of the micromeres. 



Fig. 204. Exp. 863: 2 per cent. NaCl, 2 \ 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. MgCl 2 , 9 hrs., normal 9 hrs.; many nuclei (karyomeres) and sphere! 

 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. , .... , ., , „u„, TO(TO 



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 to *™™.* 

 limited to a shallow furrow on the animal pole side of the egg; the nuclei are irregular and dense.y ^matic^ 



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 tne sp^ s - 



Fig. 212. Exp. 865: 4 per cent. NaCl, 2 hrs., normal 10 hrs.; the two macromeres hav e ^ 

 off a first and a second micromere, the first by dexiotropic and the second by Inotropic division, j* m ™ ™, 

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

 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 .^cromeres^ .T^Se 

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



spindles or tetrasters. ._ annarfttpd bv a 



Fig. 214. Exp. 846: 4 per cent. MgCl 2 , 4 hrs., normal 16 hrs.; the two mac r . om ^ e l^^S half 

 group of micromeres which have formed along both si 





les of the 1st cleavage plane; the polarity .of eacn n*u 

 ectodermal pole being the surface of ^* c ^ W £ le 



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

 and their inward rotation at the animal pole. . , . e „„„ ^th two macro- 



Fig. 215. Exp. 846: 4 per cent. MgCl 2 , 4 hrs., normal 16 hrs.; side view of an effi J™. 'Jed by the 

 meres and six micromeres; the two original micromeres of the first set have s??*™^ " ^ the macro- 

 arrows, the other two micromeres are of the 2d set; all the micromeres contain karjomeiea, 

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



