524 CELL DIVISION IN EGGS OF CREPIDULA. 



apparent reason why chromosomes are drawn together at the poles of a bipolar 

 figure, on the other hand they should repel one another and thus be scattered 

 through the cell in positions of equilibrium between the poles and the other 

 chromosomes. 



In conclusion, I do not find that the phenomena of spindle formation nor of 



chromosomal movement can be consistently explained by Lillie's or Gallardo's 



hypotheses. I find no evidence in favor of these hypotheses in experiments in which 

 an electric current is passed through dividing cells. On the other hand I find abundant 

 evidence in all my experiments that the phenomena of karyokinesis and also of 

 cytokinesis are associated with diffusion phenomena between nucleus, centrosome 

 and cell body. 



V. Effects of Abnormal Temperature. 



(Plate L. Exps. 960-961, 1170-1177.) 



Many experiments have been made on the influence of temperature on 

 development; among more recent investigations those of Driesch (1893), 0. 

 Hertwig (1890), Delage (1901), Greeley (1902), Schticking (1903), R. Lillie 

 (1908) on echinoderms, and of Rauber (1883), O. Hertwig (1896), O. Schultze 

 (1894, 1899), Lillie and Knowlton (1897), Bataillon (1903) on amphibians, must 

 be mentioned. Of work which deals primarily with the influence of altered 

 temperature on cell structure and division, the most important is that of 0. and 

 R. Hertwig (1887), who found in the sea urchin egg that a large increase of 

 temperature led to polyspermy, suppression of astral rays, even those in con- 

 nection with the sperm nucleus, lack of growth on the part of the sperm nucleus, 

 eccentricity of first cleavage spindle and unequal cleavage (Knospenfurchung) . 

 Driesch (1893) found that increased temperature led to a reduction of the 

 surface tension of the blastomeres of sea urchin eggs, to more or less separation 

 between the blastomeres and to suppression of micromere formation. Sometimes 

 the blastomeres of the 8-16 cell stages separated into two groups, thus forming 

 twins. If the temperature were increased during gastrulation, exogastrulae 

 resulted. O. Hertwig (1896) found that increased, as well as decreased, tempera- 

 ture led to the suppression of cleavage and development at the vegetal pole of 



the frog's egg. . 



The influence of decreased temperature on eggs has been studied oy v. 

 Hertwig (1890) who found in sea urchin eggs that a temperature of 2° to 3 O. 

 for a half hour led to the formation of a large reception cone ; if the eggs were 

 then warmed, a high degree of polyspermy resulted. Cold caused the disap- 

 pearance of astral rays, which quickly reappeared on warming ; it also caused e 

 degeneration and complete disappearance of the first cleavage spindle and o 

 the polar rays, while the chromatic part of the amphiaster remained unalterea^, 

 when such eggs are warmed, the spindles and polar rays appear again and divisi 

 is completed normally. By long action of cold the chromosomes are affected an ^ 

 form a reticular or vesicular nucleus. Morgan found that segmentation mig 

 be started in unfertilized eggs of Arbacia by freezing the water in which y 



