674 STUDIES IN GENERAL PHYSIOLOGY 
topterus larve, those that developed from fertilized eggs as 
well as those that developed from unfertilized eggs, died 
after two days. As the fertilized eggs developed faster 
than the unfertilized eggs, the trochophores that had devel- 
oped from the former eggs were in a more advanced stage 
at the time of death than the parthenogenetic trochophores. 
But to judge from the energy of their motion, the vitality 
of the parthenogenetic trochophores equaled that of the 
trochophores emanating from fertilized eggs.’ The cause of 
death was apparently the development of micro-organisms 
in the poorly aerated culture dishes. The parthenogenetic 
larvee of Arbacia lived, under similarly unfavorable con- 
ditions, as long as ten days. 
VI. ON THE EFFECT OF VARIOUS IONS ON THE ARTIFICIAL 
PRODUCTION OF PARTHENOGENETIC GIANT AND DWARF 
EMBRYOS IN ARBACIA AND CHETOPTERUS 
In a former paper on the artificial parthenogenesis of 
sea-urchins I have mentioned the fact that as a rule more 
than one embryo originates from one egg.” It was not un- 
usual to see 3, 4, or even 6 blastule arise from one egg. Of 
course each of these embryos was smaller than the normal 
embryo of Arbacia in which the whole mass is utilized for 
one embryo. In my first experiments I had caused the 
parthenogenetic development of the eggs of Arbacia by 
raising the osmotic pressure of the sea-water through the 
addition of MgCl,. I have since found that it depends 
upon the nature of the substance which is added to the sea- 
water whether the parthenogenetic larvee are dwarfs or of 
normal size. If the unfertilized eggs of Arbacia are put 
1JIn the following year I found that the vitality of these parthenogenetic 
larves is considerably lower than that of the larvees which came from fertilized 
eggs. [1903] 
2 Part II, p. 576. 
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