

526 CELL DIVISION IN EGGS OF CREPIDULA. 



the cleavage processes in the eggs of Crepidula. In this experiment, dishes of 



sea water containing eggs in early cleavage stages (1-8 cells) were placed on ice 

 in a refrigerator for from 4 to 40 hours, and were then fixed at once after removal 

 from the refrigerator. The temperature of the water in the dishes was a little 

 above 2° C. Figures 100-102 represent eggs which were on ice 16 hours; figures 

 103-105, eggs which were on ice 40 hours. Cleavage in these eggs was greatly 

 delayed if not entirely stopped; after 40 hours on ice many of the eggs were 

 still in the 4-cell stage. Spindle fibers and astral rays were present, though per- 

 haps less distinct than in normal eggs. 



The most characteristic feature of eggs which have been on ice from 4 to 16 

 hours is the great distinctness of the spheres which, in resting stages, appear to 

 be bounded by a definite membrane (fig. 101), and which stain so deeply that 

 they look very much like nuclei. In division stages, the spheres are surrounded 

 by coarse, chromatic granules, the sphere granules (S. G., fig. 100 et seq.), which 

 are possibly homologous with mitochondria. In the eggs which were 40 hours 

 on ice, the spheres have lost their distinctness and in their places are masses of 

 coarse sphere granules (figs. 103-105) . Apparently the centrosomes in the resting 

 stages have also disappeared and further experiments are necessary to determine 

 whether they also have broken up into granules. 



VI. Effects of Ether. 

 (Exps. 800-803, 818-819, 877-878, 1180, 1181.) 



In order to test the effects of anaesthetics on the kinetic phenomena of cell 

 division, varying quantities of ether were added to sea water in which eggs were 

 placed. With a small quantity of ether acting for a short time no effect was 



noticeable. Thus % per cent, to 1 per cent, of ether acting for J^ hr. to 1 hr. 

 produced no visible changes. However % P er cent, acting for 24 hours caused 

 the nuclei to become more densely chromatic and the spindle fibers and astral 

 rays of the mitotic figure to disappear. 1 per cent, acting 5J^ hrs. or even for 

 16 hrs. caused very few if any changes; the distribution of cytoplasm and yolk, 

 and the character of nuclei and centrosomes, whether in rest or division, are 

 apparently normal. However 1 per cent, acting for 25 hrs. produces many 

 changes ; in some cases the cleavage is very irregular and the chromatin is clumpe 

 in the resting nuclei. In division stages, many chromosomes are scattered ana 

 clumped. Nevertheless spindles and spindle fibers are present and are apparently 

 normal in structure and function. On the other hand 3 per cent, ether acting 

 for % hr. produced profound changes in the distribution of yolk and cytoplasm. 



The cytoplasm is intermingled with the yolk and vice versa, and cytoplasm ^ 

 carried in along the whole cleavage plane between macromeres. The cnro 

 somes in mitosis are often scattered along the spindle, the spindle fibers 

 disappeared, and telokinetic movements are stopped. When 3 per cent, e 

 was allowed to act for 3 hrs. and the eggs were then placed in normal sea wa e 



