588 The American Naturalist. [July, 
Omitting many interesting facts bearing upon the value of 
male and female nucleus and cell protoplasm we pass to the 
effects upon the cleavage processes. The results are similar, 
whether the drugs act to produce polyspermy or whether they 
are subsequently applied after normal fertilization. Quinine 
or chloral acting upon an egg having its cleavage nucleus in 
the spindle stage transforms this spindle into a cluster of vesi- 
cles, but if the egg is now allowed to recover in sea water the 
nucleus divides into four with the formation of four combined 
spindles. The protoplasm, however, remains affected, and 
does not follow the subsequent division of each of the four 
nuclei. 
The above work was supplemented soon after by a paper by 
Oscar Hertwig! describing the effects of cold upon the ferti- 
lization of the eggs of the sea urchin, and also recording the 
occurrence of abnormal eggs in most of the specimens found 
at Triest in the Spring of 1887; this result being apparently 
due to the unusual cold which prevented the animals collect- 
ing as usual when ripe (he finds the females discharge ova in 
the aquarium when a male has discharged sperm), and hence 
led to an overripe condition of the eggs, accompanied by sub- 
sequent abnormalities in development. 
Eggs, he finds, may be kept for several hours at a tempera- 
ture of 2° to 3°C. and yet recover, but they finally enter into 
a cold rigor. The cooling prevents the egg from forming its 
protective membrane and diminishes the receptive elevations 
upon the egg, and thus polyspermy results if the rigor does not 
intervene before the sperms have entered. Cooling after exter- 
nal fertilization may arrest the progress of the sperm, which is 
yet able to advance again when warmed. Cooling during the 
cleavage affects the nucleus so that various abnormal changes 
result, but the egg may still divide regularly when warmed, at 
least in a few cases. 
One other suggestive experiment was made, namely, the 
treatment of sea urchins’ eggs with methyl blue. This acts like 
a poison in causing polyspermy, yet weak solutions may be 
1Oscar Hertwig. Experimentelle Studien am Tierischen Ei während, und nach 
der Befruchtung. Jen. Zeit., xxiv, 1890, pp. 268-310, plates 8-10. 
