674 STUDIES IN GENERAL PHYSIOLOGY 



topterus larvae, 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. 1 The cause of 

 death was apparently the development of micro-organisms 

 in the poorly aerated culture dishes. The parthenogenetic 

 larvae 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 CH^TOPTERUS 



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. 2 It was not un- 

 usual to see 3, 4, or even 6 blastulae 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 Mg01 3 . I have since found that it depends 

 upon the nature of the substance which is added to the sea- 

 water whether the parthenogenetic larvaa are dwarfs or of 

 normal size. If the unfertilized eggs of Arbacia are put 



1 In the following year I found that the vitality of these parthenogenetic 

 larvee is considerably lower than that of the larvae which came from fertilized 

 eggs. [1903] 



2 Part II, p. 576. 



