586 The American Naturalist. [July, 
Similarly the notochord is to be regarded as double or com- 
posed of two halves, one in each of the first two cells. 
Nevertheless, M. Chabry regards the egg of Ascidia aspera 
as containing potentially but one adult, the organs of which 
seem to be localized in different parts of the egg. That this 
is necessarily true of other eggs he emphatically denies; the 
results here obtained cannot, he thinks, be extended to other 
untried cases. Granting that there is this localization of some 
organs in the ascidian egg it is evident from the author's 
account that all the structures are not divided by the first 
cleavage but rather that each cell has for the main part all 
that the other has, hence result active larve from either right 
or left cell, if the other be killed, larvee which are deficient in 
only a few organs and by no means real half-larve as the 
author calls them. 
Finally we may consider some of the experimental work 
that has been recently attempted upon eggs of lower animals, 
the echinoderms especially. 
Oscar and Richard Hertwig' subjected eggs of Strongylocen- 
trotus lividus to the action of heat, poisons and mechanical 
insult, to judge from the effects upon external and internal 
fertilization and upon cleavage as to the nature of the forces 
involved in the normal course of events. All these unusual 
agents act upon the egg so that it is unable to keep out more 
than one sperm, and hence is penetrated by several or many 
sperm, exhibiting the abnormal phenomena of polyspermy. 
Weak reagents cause only a few eggs to take in two or three 
sperms, while strong reagents cause most all the eggs to take 
in four or more sperms. The substances used and the strength 
as well as time are given in the following tables : 
WEAK REAGENTS. 
Nicotine.) icalan et drop to 1000 for 10 minutes 
Strychnine. s- 1 oo- < DORs for 20 minutes 
Morphine 660s = o a a do S. foe A hait 
10. and R. Hertwig. Ueber den Befruchtungs- und Theilungs- vorgang des their- 
ischen Eies unter dem Einfluss ausserer Agentien. Jen. Zeit. xx, 1887, pp. 120- 
227, 477-510, plates 3-9. 
