APOMIXIS 



crustacean Trichoniscus, or of the dandelion Taraxacum, arises sud- 

 denly owing to the fertilization of an egg with the unreduced 

 1 6 chromosomes by a normal sperm with 8 (or vice versa). Such 

 a triploid, although only a number-hybrid, suffers all the misfortunes 

 of the authentic fruit of cross-fertilization. The lagging of unpaired 



ARTEMIA 5ALINA 



Sexual ->- Parthenogenetic 



(l)subsexual 



2x nnnnnn □□□ 



nnnnDD □□□ 



Mediterraneans N.America 



3x 



S.France £- Egypt 



Portorose 



4x 



D 



Odessa 



(2)non- sexual 





Mediterranean 



8x 





3 





Fig. 66. — Evolution of sexual, sub-sexual and non-sexual forms in the brine shrimp 

 Artemia salina. The sub-sexual forms have meiosis followed by fusion of its products. 

 The non-sexual ones suppress both meiosis and fusion: the unreduced egg develops. 

 Each square represents a tested location (after Barigozzi, 1946). 



chromosomes at meiosis in its mother cells prevents the separation 

 of the two daughter nuclei. A single restitution nucleus is reformed 

 with the whole triploid complement. The second division then 

 follows its normal course and two triploid nuclei are formed. In 

 other words the reduction of chromosome number is evaded and 

 a female germ cell formed in this way, and developing as it often 

 can, especially if unreduced, without fertihzation, reproduces its 



265 



