ix] FERTILISATION BY POLAR NUCLEUS 129 



BRAUER in the Phyllopod Artemia, and has subsequently 

 been observed in a few other cases. BRAUER stated that in 

 some eggs of Artemia, instead of the usual production of 

 only one polar body without reduction, two polar divisions 

 took place, presumably with reduction of chromosomes. 

 The second polar nucleus, however, instead of being thrown 

 out of the egg, remained in it, and after a time sank back 

 from the surface of the egg towards the egg nucleus and 

 the two conjugated exactly as the sperm nucleus conjugates 

 with the egg nucleus of a fertilised egg. The polar nucleus 

 thus took the place of a sperm nucleus, and the egg may be 

 said to be fertilised by one of its own polar nuclei. Con- 

 firmation of BRAUER' s statement was for a longtime lacking, 

 and doubt was cast upon its correctness, although investiga- 

 tions intended to settle the matter showed the existence of 

 other curious facts in Artemia. For example, ARTOM finds 

 that a race from Capodistria on the Adriatic has a somatic 

 number of 84 chromosomes and is always parthenogenetic, 

 while the race found at Cagliari in Sardinia has 42 chromo- 

 somes in its somatic nuclei, which are consequently half 

 the size and twice as numerous, and this race always repro- 

 duces sexually. Subsequently to BRAUER'S paper other 

 observers have discovered a similar fertilisation by the 

 second polar body in two or three cases by BRUES in 

 Xenos, an insect of the family Stylopidae, and BUCHNER 

 (1911) in eggs of a starfish made to develop parthenogene- 

 tically by treatment with carbon dioxide, while more 

 recently Miss MORRIS has made similar observations on the 

 eggs of the Mollusc Cumingia caused to develop partheno- 

 genetically. Among plants also a similar process has been 

 described by ROSENBERG in Hieracium, so that the phenom- 

 enon of fertilisation by the second polar nucleus may be 

 regarded as established, at least in rare cases. 



D. C. 9 



